No files shown after upgrade to NC27

Nextcloud version: 27.0.1
Operating system and version (eg, Ubuntu 20.04): Debian bookworm
Apache or nginx version (eg, Apache 2.4.25): nginx 1.22.1-9
PHP version (eg, 7.4): 8.2

The issue you are facing:

After upgrade i don’t see any files in the Files application. There is no (+) button to create a directory. If i disable the fancy “Recommendations” app, the view is completely empty. If i keep the app, then i do see some recommended files (recently edited), but they either can’t be interacted with, or trying to open them sends the browser into a loop.

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

Steps to replicate it:

  1. Upgrade Nextcloud from 25.0.9 to 26.x.x to 27.0.1

The output of your Nextcloud log in Admin > Logging:

2023-07-26T15:19:43.067505+03:00 servername Nextcloud[2851971]: {"reqId":"0Oeihllc7Dx8i4OO5eTl","level":3,"time":"2023-07-26T12:19:43+00:00","remoteAddr":"myipaddress","user":"admin","app":"index","method":"GET","url":"/apps/theming/icon/dashboard?v=d00160d2","message":"{\"Exception\":\"OCP\\\\Files\\\\NotPermittedException\",\"Message\":\"Could not create folder \\\"/appdata_oc3l8nl6sagi/theming/global/16\\\"\",\"Code\":0,\"Trace\":[{\"file\":\"/home/nextcloud/lib/private/Files/SimpleFS/SimpleFolder.php\",\"line\":105,\"function\":\"newFolder\",\"class\":\"OC\\\\Files\\\\Node\\\\Folder\",\"type\":\"->\"},{\"file\":\"/home/nextcloud/apps/theming/lib/ImageManager.php\",\"line\":175,\"function\":\"newFolder\",\"class\":\"OC\\\\Files\\\\SimpleFS\\\\SimpleFolder\",\"type\":\"->\"},{\"file\":\"/home/nextcloud/apps/theming/lib/ImageManager.php\",\"line\":190,\"function\":\"getCacheFolder\",\"class\":\"OCA\\\\Theming\\\\ImageManager\",\"type\":\"->\"},{\"file\":\"/home/nextcloud/apps/theming/lib/Controller/IconController.php\",\"line\":163,\"function\":\"getCachedImage\",\"class\":\"OCA\\\\Theming\\\\ImageManager\",\"type\":\"->\"},{\"function\":\"getTouchIcon\",\"class\":\"OCA\\\\Theming\\\\Controller\\\\IconController\",\"type\":\"->\"},{\"file\":\"/home/nextcloud/lib/private/AppFramework/Http/Dispatcher.php\",\"line\":230,\"function\":\"call_user_func_array\"},{\"file\":\"/home/nextcloud/lib/private/AppFramework/Http/Dispatcher.php\",\"line\":137,\"function\":\"executeController\",\"class\":\"OC\\\\AppFramework\\\\Http\\\\Dispatcher\",\"type\":\"->\"},{\"file\":\"/home/nextcloud/lib/private/AppFramework/App.php\",\"line\":183,\"function\":\"dispatch\",\"class\":\"OC\\\\AppFramework\\\\Http\\\\Dispatcher\",\"type\":\"->\"},{\"file\":\"/home/nextcloud/lib/private/Route/Router.php\",\"line\":315,\"function\":\"main\",\"class\":\"OC\\\\AppFramework\\\\App\",\"type\":\"::\"},{\"file\":\"/home/nextcloud/lib/base.php\",\"line\":1071,\"function\":\"match\",\"class\":\"OC\\\\Route\\\\Router\",\"type\":\"->\"},{\"file\":\"/home/nextcloud/index.php\",\"line\":36,\"function\":\"handleRequest\",\"class\":\"OC\",\"type\":\"::\"}],\"File\":\"/home/nextcloud/lib/private/Files/Node/Folder.php\",\"Line\":162,\"CustomMessage\":\"--\"}","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0","version":"27.0.1.2"}

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

<?php
$CONFIG = array (
  'instanceid' => 'oc3l8nl6sagi',
  'passwordsalt' => 'foo',
  'secret' => 'bar',
  'trusted_domains' =>
  array (
    0 => 'my domain name',
  ),
  'datadirectory' => '/mnt/nextcloud_data',
  'dbtype' => 'mysql',
  'version' => '27.0.1.2',
  'overwrite.cli.url' => 'https://my domain name',
  'htaccess.RewriteBase' => '/',
  'dbname' => 'nextcloud',
  'dbhost' => 'localhost:/var/run/mysqld/mysqld.sock',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'database login',
  'dbpassword' => 'database password',
  'installed' => true,
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'mail_domain' => 'my mail domain name',
  'mail_from_address' => 'postmaster',
  'mail_smtpmode' => 'smtp',
  'mail_sendmailmode' => 'smtp',
  'mail_smtphost' => 'my mail domain name',
  'mail_smtpport' => '587',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtpauth' => 1,
  'mail_smtpname' => 'mail login',
  'mail_smtppassword' => 'mail password',
  'mail_smtpsecure' => 'tls',
  'maintenance' => false,
  'theme' => '',
  'loglevel' => 2,
  'log_type' => 'syslog',
  'logfile' => '',
  'syslog_tag' => 'Nextcloud',
  'updater.secret' => 'some random symbols',
  'updater.release.channel' => 'stable',
);

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

myclientipaddress - - [26/Jul/2023:15:42:00 +0300] "GET /apps/files/files HTTP/2.0" 200 12314 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0"
myclientipaddress - - [26/Jul/2023:15:42:02 +0300] "GET /ocs/v2.php/search/providers?from=%2Fapps%2Ffiles%2Ffiles HTTP/2.0" 200 203 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0"
myclientipaddress - - [26/Jul/2023:15:42:03 +0300] "GET /ocs/v2.php/apps/notifications/api/v2/notifications HTTP/2.0" 200 81 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0"
myclientipaddress - - [26/Jul/2023:15:42:03 +0300] "GET /apps/files_sharing/api/externalShares HTTP/2.0" 200 22 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0"
myclientipaddress - - [26/Jul/2023:15:42:03 +0300] "PROPFIND /remote.php/dav/files/admin/ HTTP/2.0" 400 249 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0"
myclientipaddress - - [26/Jul/2023:15:42:05 +0300] "GET /apps/files/api/v1/stats HTTP/2.0" 200 158 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0"
nginx error.log is empty

Miraculously fixed by completely uninstalling php8.2, installing php8.3 (turned out to be a mistake, Nextcloud doesn’t support it), and re-installing php8.2 again.

Just want to jump in and say this happened to me as well. After upgrade from 26.0.4 to 27.0.1 the files app is completely broken and just shows a blank screen. The other apps seem to be working fine but the files app is why I use NC.
I guess I could install php8.3 then re-install php8.2.

Update: Got it working. The installer warned me that app ‘epubreader’ had no compatible version and would be disabled. In fact, after the upgrade the app was still enabled, and was filling the system logs with errors. After disabling and removing the ‘epubreader’ app my files app is working again. Another miracle.

Is the app 'epubreader' listed in your config.php:

  'app_install_overwrite' => 
  array (
    0 => 'epubreader',
  ),

hope that give clarity,
much luck!