Mail APP: Blank page

Nextcloud version: 25.0.2-1 (installation from repository)
Operating system and version: Manjaro Linux 22 (Arch Linux based)
Apache or nginx version: apache 2.4.54-3
PHP version : 8.1.13-4

The issue you are facing:

Is this the first time you’ve seen this error?: Yes

Steps to replicate it:

  1. Open Mail app page
  2. Observe “blank” page
  3. Sorrow

This is first time I’m trying Mail app, so I don’t know if it worked before.

By “blank” page I mean, that top menu header is OK, page background is loaded, but app contents are missing.

I did a small investigation, and this is what I have discovered: there are javascript errors when loading mail app page.

Resource with "https://pik-pik.ee/nextcloud/wapps/mail/js/mail.546.1526a0a69ddee1dd333c.js" was blocked due to mismatch of MIME type ("text/html") (X-Content-Type -Options: sniff).
Resource with "https://pik-pik.ee/nextcloud/wapps/mail/js/mail.276.e6df2ff30581b285ab09.js" was blocked due to mismatch of MIME type ("text/html") (X-Content-Type -Options: sniff).

This is due, that these files are missing, and what it actually loads is a page that redirects to login page, that’s why it is text/html. I can see that also in apache access logs:

84.52.56.150 - - [02/Jan/2023:13:57:54 +0200] "GET /nextcloud/wapps/mail/js/mail.546.1526a0a69ddee1dd333c.js HTTP/1.1" 404 - "-" "Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"
84.52.56.150 - - [02/Jan/2023:13:57:54 +0200] "GET /nextcloud/wapps/mail/js/mail.276.e6df2ff30581b285ab09.js HTTP/1.1" 404 - "-" "Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"

I checked the folder that contains these script files:

[pik-pik js]# ls -l
итого 35744
-rw-r--r-- 1 nextcloud nextcloud     206 24. dets  16:21 2e4d3cbdb67ee5310028.svg
-rw-r--r-- 1 nextcloud nextcloud     168 24. dets  16:21 2eaf8b262f4672598c6a.svg
-rw-r--r-- 1 nextcloud nextcloud     230 24. dets  16:21 autoredirect.js
-rw-r--r-- 1 nextcloud nextcloud     854 24. dets  16:21 autoredirect.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud    1344 24. dets  16:21 autoredirect.js.map
-rw-r--r-- 1 nextcloud nextcloud 1107428 24. dets  16:21 dashboard.js
-rw-r--r-- 1 nextcloud nextcloud   14879 24. dets  16:21 dashboard.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud 3533380 24. dets  16:21 dashboard.js.map
-rw-r--r-- 1 nextcloud nextcloud  109924 24. dets  16:21 googleoauthpopup.js
-rw-r--r-- 1 nextcloud nextcloud     864 24. dets  16:21 googleoauthpopup.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud  632381 24. dets  16:21 googleoauthpopup.js.map
-rw-r--r-- 1 nextcloud nextcloud   19973 24. dets  16:21 htmlresponse.js
-rw-r--r-- 1 nextcloud nextcloud     840 24. dets  16:21 htmlresponse.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud   77333 24. dets  16:21 htmlresponse.js.map
-rw-r--r-- 1 nextcloud nextcloud  279788 24. dets  16:21 mail.177.b13c0349e9565e741e8a.js
-rw-r--r-- 1 nextcloud nextcloud  408837 24. dets  16:21 mail.177.b13c0349e9565e741e8a.js.map
-rw-r--r-- 1 nextcloud nextcloud    4294 24. dets  16:21 mail.276.fd241c4b3959c51d0f15.js
-rw-r--r-- 1 nextcloud nextcloud   11003 24. dets  16:21 mail.276.fd241c4b3959c51d0f15.js.map
-rw-r--r-- 1 nextcloud nextcloud  595636 24. dets  16:21 mail.462.9d85d64cc762fbe8cbec.js
-rw-r--r-- 1 nextcloud nextcloud    4436 24. dets  16:21 mail.462.9d85d64cc762fbe8cbec.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud 1018267 24. dets  16:21 mail.462.9d85d64cc762fbe8cbec.js.map
-rw-r--r-- 1 nextcloud nextcloud 4605605 24. dets  16:21 mail.489.8245318d2ed2e021bfce.js
-rw-r--r-- 1 nextcloud nextcloud    3946 24. dets  16:21 mail.489.8245318d2ed2e021bfce.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud 9640429 24. dets  16:21 mail.489.8245318d2ed2e021bfce.js.map
-rw-r--r-- 1 nextcloud nextcloud  366708 24. dets  16:21 mail.546.fe28e799fec76c813af2.js
-rw-r--r-- 1 nextcloud nextcloud    5058 24. dets  16:21 mail.546.fe28e799fec76c813af2.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud  523973 24. dets  16:21 mail.546.fe28e799fec76c813af2.js.map
-rw-r--r-- 1 nextcloud nextcloud 1507455 24. dets  16:21 mail.754.79474d1440a7f51955ec.js
-rw-r--r-- 1 nextcloud nextcloud    1034 24. dets  16:21 mail.754.79474d1440a7f51955ec.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud 2942657 24. dets  16:21 mail.754.79474d1440a7f51955ec.js.map
-rw-r--r-- 1 nextcloud nextcloud 1574424 24. dets  16:21 mail.js
-rw-r--r-- 1 nextcloud nextcloud   12201 24. dets  16:21 mail.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud 4930746 24. dets  16:21 mail.js.map
-rw-r--r-- 1 nextcloud nextcloud  638573 24. dets  16:21 settings.js
-rw-r--r-- 1 nextcloud nextcloud    1941 24. dets  16:21 settings.js.LICENSE.txt
-rw-r--r-- 1 nextcloud nextcloud 1941726 24. dets  16:21 settings.js.map
drwxr-xr-x 2 nextcloud nextcloud    4096 24. dets  16:21 translations
[pik-pik js]# pwd
/var/lib/nextcloud/apps/mail/js
[pik-pik js]#

The folder does contain mail.546.*.js and mail.276.*.js files, but they have different hash values. I don’t know what these mean.

Why Nextcloud requests javascript files with wrong hash values?

I could kinda copy or make a symbolic link to match requested file, but this would just heal symptoms, not the root cause.

I have a guess, that at some point upgrade process messed up. I started using since around version nextcloud-18.0.4 and kept updating to this date.

Please support =^.^= uwu




The output of your Nextcloud log in Admin > Logging:

log viewer is broken currently, (https://github.com/nextcloud/logreader/issues/699)
so i paste piece of nextcloud.log file,
when mail app page requested:

{"reqId":"Y7LE04t_ClLsrzUlaAIaJgAAAAo","level":0,"time":"2023-01-02T11:49:39+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"PROPFIND","url":"/nextcloud/remote.php/dav/files/ValkaTR/","message":"/appinfo/app.php is deprecated, use \\OCP\\AppFramework
\\Bootstrap\\IBootstrap on the application class instead.","userAgent":"Mozilla/5.0 (Linux) mirall/3.6.4git (Nextcloud, manjaro-6.1.0-1-MAN
JARO ClientArchitecture: x86_64 OsArchitecture: x86_64)","version":"25.0.2.3","data":{"app":"music"}}                                      
{"reqId":"Y7LE04AyQwP7IPbOBJtxBQAAAAg","level":0,"time":"2023-01-02T11:49:39+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"GET","url":"/nextcloud/apps/mail/","message":"/appinfo/app.php is deprecated, use \\OCP\\AppFramework\\Bootstrap\\IBootstrap 
on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0","version":"25.0.2.3
","data":{"app":"music"}}                                                                                                                  
{"reqId":"Y7LE1IAyQwP7IPbOBJtxBgAAAAg","level":0,"time":"2023-01-02T11:49:40+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"GET","url":"/nextcloud/apps/theming/image/logoheader?v=6","message":"/appinfo/app.php is deprecated, use \\OCP\\AppFramework\
\Bootstrap\\IBootstrap on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108
.0","version":"25.0.2.3","data":{"app":"music"}}                                                                                           
{"reqId":"Y7LE1IAyQwP7IPbOBJtxBwAAAAg","level":0,"time":"2023-01-02T11:49:40+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"GET","url":"/nextcloud/ocs/v2.php/search/providers?from=%2Fnextcloud%2Fapps%2Fmail%2F","message":"/appinfo/app.php is depreca
ted, use \\OCP\\AppFramework\\Bootstrap\\IBootstrap on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.
0) Gecko/20100101 Firefox/108.0","version":"25.0.2.3","data":{"app":"music"}}                                                              
{"reqId":"Y7LE1IAyQwP7IPbOBJtxCAAAAAg","level":0,"time":"2023-01-02T11:49:40+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"GET","url":"/nextcloud/ocs/v2.php/apps/notifications/api/v2/notifications","message":"/appinfo/app.php is deprecated, use \\O
CP\\AppFramework\\Bootstrap\\IBootstrap on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/201
00101 Firefox/108.0","version":"25.0.2.3","data":{"app":"music"}}                                                                          
{"reqId":"Y7LE1JdURzqUUsJBdWT10AAAAAI","level":0,"time":"2023-01-02T11:49:40+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"PUT","url":"/nextcloud/ocs/v2.php/apps/user_status/api/v1/heartbeat?format=json","message":"/appinfo/app.php is deprecated, u
se \\OCP\\AppFramework\\Bootstrap\\IBootstrap on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gec
ko/20100101 Firefox/108.0","version":"25.0.2.3","data":{"app":"music"}}                                                                    
{"reqId":"Y7LE1NsFNLmhd-K80pC-CAAAAAc","level":0,"time":"2023-01-02T11:49:40+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"GET","url":"/nextcloud/wapps/mail/js/mail.546.1526a0a69ddee1dd333c.js","message":"/appinfo/app.php is deprecated, use \\OCP\\
AppFramework\\Bootstrap\\IBootstrap on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/2010010
1 Firefox/108.0","version":"25.0.2.3","data":{"app":"music"}}                                                                              
{"reqId":"Y7LE1B3MWAam7F7-Lv8PLAAAAAA","level":0,"time":"2023-01-02T11:49:41+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"GET","url":"/nextcloud/wapps/mail/js/mail.276.e6df2ff30581b285ab09.js","message":"/appinfo/app.php is deprecated, use \\OCP\\
AppFramework\\Bootstrap\\IBootstrap on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/2010010
1 Firefox/108.0","version":"25.0.2.3","data":{"app":"music"}}                                                                              
{"reqId":"Y7LE1JdURzqUUsJBdWT10QAAAAI","level":0,"time":"2023-01-02T11:49:41+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"PROPFIND","url":"/nextcloud/remote.php/dav/","message":"/appinfo/app.php is deprecated, use \\OCP\\AppFramework\\Bootstrap\\I
Bootstrap on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0","version"
:"25.0.2.3","data":{"app":"music"}}
{"reqId":"Y7LE1YAyQwP7IPbOBJtxCQAAAAg","level":0,"time":"2023-01-02T11:49:41+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"PROPFIND","url":"/nextcloud/remote.php/dav/principals/users/ValkaTR/","message":"/appinfo/app.php is deprecated, use \\OCP\\A
ppFramework\\Bootstrap\\IBootstrap on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101
 Firefox/108.0","version":"25.0.2.3","data":{"app":"music"}}                                                                               
{"reqId":"Y7LE1YAyQwP7IPbOBJtxCgAAAAg","level":0,"time":"2023-01-02T11:49:42+00:00","remoteAddr":"84.52.56.150","user":"ValkaTR","app":"mus
ic","method":"PROPFIND","url":"/nextcloud/remote.php/dav/calendars/ValkaTR/","message":"/appinfo/app.php is deprecated, use \\OCP\\AppFrame
work\\Bootstrap\\IBootstrap on the application class instead.","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefo
x/108.0","version":"25.0.2.3","data":{"app":"music"}}

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

<?php
$CONFIG = array (
  'instanceid' => '############',
  'passwordsalt' => '##############################',
  'secret' => '################################################',
  'trusted_domains' => 
  array (
    0 => 'pik-pik.ee'
  ),
  'datadirectory' => '/var/nextcloud',
  'dbtype' => 'mysql',
  'version' => '25.0.2.3',
  'overwrite.cli.url' => 'http://pik-pik.ee/nextcloud',
  'htaccess.RewriteBase' => '/nextcloud',
  'dbname' => '#############',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => '#############',
  'dbpassword' => '#############',
  'installed' => true,
  'theme' => '',
  'loglevel' => 0,
  'logfile' => '/var/log/nextcloud/nextcloud.log',
  'maintenance' => false,
  'mail_from_address' => 'admin',
  'mail_smtpmode' => 'smtp',
  'mail_sendmailmode' => 'smtp',
  'mail_domain' => 'pik-pik.ee',
  'enable_previews' => true,
  'enabledPreviewProviders' => 
  array (
    0 => 'OC\\Preview\\TXT',
    1 => 'OC\\Preview\\MarkDown',
    2 => 'OC\\Preview\\OpenDocument',
    3 => 'OC\\Preview\\PDF',
    4 => 'OC\\Preview\\MSOffice2003',
    5 => 'OC\\Preview\\MSOfficeDoc',
    6 => 'OC\\Preview\\Image',
    7 => 'OC\\Preview\\Photoshop',
    8 => 'OC\\Preview\\TIFF',
    9 => 'OC\\Preview\\SVG',
    10 => 'OC\\Preview\\Font',
    11 => 'OC\\Preview\\MP3',
    12 => 'OC\\Preview\\Movie',
    13 => 'OC\\Preview\\MKV',
    14 => 'OC\\Preview\\MP4',
    15 => 'OC\\Preview\\AVI',
  ),
  'apps_paths' => 
  array (
    0 => 
    array (
      'path' => '/usr/share/webapps/nextcloud/apps',
      'url' => '/apps',
      'writable' => false,
    ),
    1 => 
    array (
      'path' => '/var/lib/nextcloud/apps',
      'url' => '/wapps',
      'writable' => true,
    ),
  ),
  'app_install_overwrite' => 
  array (
    0 => 'music',
  ),
  'mail_smtphost' => 'pik-pik.ee',
  'mail_smtpport' => '587',
  'mail_smtpsecure' => 'tls',
  'mail_smtpauth' => 1,
  'mail_smtpname' => '###############',
  'mail_smtppassword' => '##################',
);

The output of your Apache/nginx/system log in /var/log/____:

84.52.56.150 - - [02/Jan/2023:13:57:52 +0200] "GET /nextcloud/apps/mail/ HTTP/1.1" 200 13701 "-" "Mozilla/5.0 (X11; Linux x86_64; rv:108.0)
 Gecko/20100101 Firefox/108.0"                                                                                                             
84.52.56.150 - - [02/Jan/2023:13:57:53 +0200] "GET /nextcloud/apps/theming/image/logoheader?v=6 HTTP/1.1" 404 31006 "-" "Mozilla/5.0 (X11; 
Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                                      
84.52.56.150 - - [02/Jan/2023:13:57:53 +0200] "GET /nextcloud/dist/core-common.js.map?v=c696e133421bbeb9dc14 HTTP/1.1" 304 - "-" "Mozilla/5
.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                             
84.52.56.150 - - [02/Jan/2023:13:57:53 +0200] "GET /nextcloud/ocs/v2.php/search/providers?from=%2Fnextcloud%2Fapps%2Fmail%2F HTTP/1.1" 200 
409 "-" "Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                           
84.52.56.150 - - [02/Jan/2023:13:57:53 +0200] "PUT /nextcloud/ocs/v2.php/apps/user_status/api/v1/heartbeat?format=json HTTP/1.1" 200 129 "-
" "Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                 
84.52.56.150 - - [02/Jan/2023:13:57:53 +0200] "GET /nextcloud/ocs/v2.php/apps/notifications/api/v2/notifications HTTP/1.1" 200 558 "-" "Moz
illa/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                       
84.52.56.150 - - [02/Jan/2023:13:57:53 +0200] "GET /nextcloud/apps/theming/image/logoheader?v=6 HTTP/1.1" 404 31006 "-" "Mozilla/5.0 (X11; 
Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                                      
84.52.56.150 - - [02/Jan/2023:13:57:54 +0200] "GET /nextcloud/wapps/mail/js/mail.546.1526a0a69ddee1dd333c.js HTTP/1.1" 404 - "-" "Mozilla/5
.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                             
84.52.56.150 - - [02/Jan/2023:13:57:54 +0200] "GET /nextcloud/wapps/mail/js/mail.276.e6df2ff30581b285ab09.js HTTP/1.1" 404 - "-" "Mozilla/5
.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                             
84.52.56.150 - - [02/Jan/2023:13:57:54 +0200] "PROPFIND /nextcloud/remote.php/dav/ HTTP/1.1" 207 236 "-" "Mozilla/5.0 (X11; Linux x86_64; r
v:108.0) Gecko/20100101 Firefox/108.0"                                                                                                     
84.52.56.150 - - [02/Jan/2023:13:57:54 +0200] "PROPFIND /nextcloud/remote.php/dav/principals/users/ValkaTR/ HTTP/1.1" 207 710 "-" "Mozilla/
5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                            
84.52.56.150 - - [02/Jan/2023:13:57:55 +0200] "GET /nextcloud/apps/viewer/js/viewer-main.js.map?v=1c9fb1762206f91e2b47 HTTP/1.1" 304 - "-" 
"Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                   
84.52.56.150 - - [02/Jan/2023:13:57:55 +0200] "GET /nextcloud/wapps/richdocuments/js/richdocuments-viewer.js.map?v=75a18a4eb1c38903e22e HTT
P/1.1" 304 - "-" "Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                  
84.52.56.150 - - [02/Jan/2023:13:57:55 +0200] "GET /nextcloud/apps/text/js/text-viewer.js.map?v=4a5e8b07b5ca655190cf HTTP/1.1" 304 - "-" "M
ozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                     
84.52.56.150 - - [02/Jan/2023:13:57:55 +0200] "GET /nextcloud/apps/notifications/js/notifications-main.js.map?v=64314571dd6f8477ff87 HTTP/1
.1" 304 - "-" "Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                     
84.52.56.150 - - [02/Jan/2023:13:57:55 +0200] "GET /nextcloud/dist/core-main.js.map?v=925f3f6cf2d1e7fc1152 HTTP/1.1" 304 - "-" "Mozilla/5.0
 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"                                                                               
84.52.56.150 - - [02/Jan/2023:13:57:55 +0200] "GET /nextcloud/apps/mail/js/mail.js.map HTTP/1.1" 304 - "-" "Mozilla/5.0 (X11; Linux x86_64;
 rv:108.0) Gecko/20100101 Firefox/108.0"                                                                                                   
84.52.56.150 - - [02/Jan/2023:13:57:54 +0200] "PROPFIND /nextcloud/remote.php/dav/calendars/ValkaTR/ HTTP/1.1" 207 1687 "-" "Mozilla/5.0 (X
11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0"

Investigation update:

I have two nearly identical folders for mail app:

/usr/share/webapps/nextcloud/apps/mail/
(https://localhost/nextcloud/apps/mail/)

/var/lib/nextcloud/apps/mail/
(https://localhost/nextcloud/wapps/mail/)

The difference is these javascript files, that mail app cannot load:

[pik-pik js]# LC_ALL="C" diff -q /usr/share/webapps/nextcloud/apps/mail/js/ /var/lib/nextcloud/apps/mail/js/
Only in /usr/share/webapps/nextcloud/apps/mail/js/: mail.276.e6df2ff30581b285ab09.js
Only in /usr/share/webapps/nextcloud/apps/mail/js/: mail.276.e6df2ff30581b285ab09.js.map
Only in /var/lib/nextcloud/apps/mail/js/: mail.276.fd241c4b3959c51d0f15.js
Only in /var/lib/nextcloud/apps/mail/js/: mail.276.fd241c4b3959c51d0f15.js.map
Only in /usr/share/webapps/nextcloud/apps/mail/js/: mail.546.1526a0a69ddee1dd333c.js
Only in /usr/share/webapps/nextcloud/apps/mail/js/: mail.546.1526a0a69ddee1dd333c.js.LICENSE.txt
Only in /usr/share/webapps/nextcloud/apps/mail/js/: mail.546.1526a0a69ddee1dd333c.js.map
Only in /var/lib/nextcloud/apps/mail/js/: mail.546.fe28e799fec76c813af2.js
Only in /var/lib/nextcloud/apps/mail/js/: mail.546.fe28e799fec76c813af2.js.LICENSE.txt
Only in /var/lib/nextcloud/apps/mail/js/: mail.546.fe28e799fec76c813af2.js.map
Files /usr/share/webapps/nextcloud/apps/mail/js/mail.js and /var/lib/nextcloud/apps/mail/js/mail.js differ
Files /usr/share/webapps/nextcloud/apps/mail/js/mail.js.map and /var/lib/nextcloud/apps/mail/js/mail.js.map differ
Common subdirectories: /usr/share/webapps/nextcloud/apps/mail/js/translations and /var/lib/nextcloud/apps/mail/js/translations
[pik-pik js]#

ok, so symbolic links did indeed fix the issue:

# ln -s -v /usr/share/webapps/nextcloud/apps/mail/js/mail.276.e6df2ff30581b285ab09.js /var/lib/nextcloud/apps/mail/js/mail.276.e6df2ff30581b285ab09.js
# ln -s -v /usr/share/webapps/nextcloud/apps/mail/js/mail.276.e6df2ff30581b285ab09.js.map /var/lib/nextcloud/apps/mail/js/mail.276.e6df2ff30581b285ab09.js.map
# ln -s -v /usr/share/webapps/nextcloud/apps/mail/js/mail.546.1526a0a69ddee1dd333c.js /var/lib/nextcloud/apps/mail/js/mail.546.1526a0a69ddee1dd333c.js
# ln -s -v /usr/share/webapps/nextcloud/apps/mail/js/mail.546.1526a0a69ddee1dd333c.js.map /var/lib/nextcloud/apps/mail/js/mail.546.1526a0a69ddee1dd333c.js.map
# ln -s -v /usr/share/webapps/nextcloud/apps/mail/js/mail.546.1526a0a69ddee1dd333c.js.LICENSE.txt /var/lib/nextcloud/apps/mail/js/mail.546.1526a0a69ddee1dd333c.js.LICENSE.txt

the mail app is now working,
but what the hell is going on here?