Etag issue on sync and can't delete files locally

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Nextcloud version (eg, 18.0.2): 20.0.4
Operating system and version (eg, Ubuntu 20.04): Ubuntu 20.04
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.41
PHP version (eg, 7.1): 7.4

The issue you are facing:
I connected a client via the fedora 33 nextcloud client package to a freshly installed server, but got some errors on file sync:
No E-Tag received from server, check Proxy/Gateway

it seems this error occured for all files that have a space in their name. Also, via the web interface, I can’t open these files nor delete them. The files that have the issue are all the standard files upon installation with a space in their name:
Documents/Nextcloud flyer.pdf
Documents/Welcome to Nextcloud Hub.docx
Photos/Nextcloud community.jpg
etc …

Is this the first time you’ve seen this error? (Y/N): Y

Steps to replicate it:

  1. install nextcloud server
  2. install client
  3. sync

The output of your Nextcloud log in Admin > Logging:

Nothing really relevant in this log

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

  'memcache.local' => '\\OC\\Memcache\\APCu',

(nothing else of interest, this is a clean installation)

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

- - [23/Dec/2020:01:00:32 +0100] "GET /remote.php/dav/files/92834fec-0b58-102c-8329-dd07bde33ea1/Documents/Nextcloud%20flyer.pdf HTTP/1.1" 200 1746 "-" "Mozilla/5.0 (Linux) mirall/2.6.5git (Nextcloud)"

(I showed 1 get line for a file with spaces, no errors, also nothing in the php-fpm logs).
I know other tickets exist with the same problem, but I don’t have litespeed nor is it linked to certain extensions (one image with a space has it, the others don’t).
My virtual host config in apache:

<VirtualHost *:443>
    DocumentRoot /var/www/nextcloud/nextcloud-html
    ServerName  xxxxx
    <Directory /var/www/nextcloud/nextcloud-html>
        Require all granted
        AllowOverride All
        Options FollowSymLinks MultiViews
        <IfModule mod_dav.c>
            Dav off
        </IfModule>
    </Directory>
    ProxyPassMatch ^/(.*\.php(/.*)?)$ fcgi://127.0.0.1:9010/var/www/nextcloud/nextcloud-html/$1
    Header always set Strict-Transport-Security "max-age=63072000; includeSubdomains;"

SSLCertificateFile /etc/letsencrypt/live/xxx/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/xxx/privkey.pem
Include /etc/letsencrypt/options-ssl-apache.conf
</VirtualHost>

Putting local files in the synced folder is the same issue: files without spaces get synced ok, files with spaces have issues upon syncing to the remote nextcloud server: “the server did not acknowledge the last chunk. (No E-Tag was present)”

Ok, found the issue (thanks to looking further to tickets mentioning space issues).
it seems apache should have this config:

<FilesMatch \.php$>
  SetHandler "proxy:fcgi://127.0.0.1:9010"
</FilesMatch>

(or use LocationMatch if you like that, sometimes better)
and not:

    ProxyPassMatch ^/(.*\.php(/.*)?)$ fcgi://127.0.0.1:9010/var/www/nextcloud/nextcloud-html/$1