Webinterface unreponsive, nextcloud.log empty

Nextcloud version: 23.0.0.10
Operating system and version: Linux version 3.10.105 (root@build2) (gcc version 4.9.3 20150311 (prerelease) (crosstool-NG 1.20.0) ) #25556 SMP Sat Aug 28 02:15:10 CST 2021
nginx version: nginx/1.20.2
PHP version: 7.4.26

I have a docker install (linuxserver/nextcloud) of nextcloud with a mysql database. It has not been working properly since install. The host machine is a Synology DS412+.

The first login after a server restart works and the Dashboard loads. After that, the webinterface becomes unresponsive.

Nothing is written to the log file.

I have tried reinstalling with the same outcome. I have another installation on a different server, using the same docker image, which is working fine. I have compared the config files and nothing seems out of place.

The output of your Nextcloud log in Admin > Logging:
Web interface not responding

Do you have any ideas how to debug this problem?
Thank you for your help
FMann

Config and logs:

The output of your config.php:

<?php                                                                                                                                            
$CONFIG = array (                                                                                                                                
  'memcache.local' => '\\OC\\Memcache\\APCu',                                                                                                    
  'datadirectory' => '/data',                                                                                                                    
  'instanceid' => '',                                                                                                                
  'passwordsalt' => '',                                                                                            
  'secret' => '',                                                                                
  'trusted_domains' =>                                                                                                                           
  array (                                                                                                                                        
    0 => 'localhost',                                                                                                                            
    1 => 'sub.domain.tld',                                                                                                               
  ),                                                                                                                                             
  'trusted_proxies' =>                                                                                                                           
  array(                                                                                                                                         
    0 => 'swag',                                                                                                                                 
  ),                                                                                                                                             
  'overwrite.cli.url' => 'https://sub.domain.tld',                                                                                       
  'overwritehost' => 'sub.domain.tld',                                                                                                   
  'overwriteprotocol' => 'https',                                                                                                                
  'dbtype' => 'mysql',                                                                                                                           
  'version' => '23.0.0.10',                                                                                                                      
  'dbname' => 'dbname',                                                                                                                       
  'dbhost' => 'dbhost',                                                                                                                     
  'dbport' => '',                                                                                                                                
  'dbtableprefix' => 'oc_',                                                                                                                      
  'mysql.utf8mb4' => true,                                                                                                                       
  'dbuser' => 'dbuser',                                                                                                                       
  'dbpassword' => 'password',                                                                                                            
  'installed' => true,                                                                                                                           
  'loglevel' => 1,
  'log_type' => 'file',                                                                                                                          
  'logfile' => 'nextcloud.log',                                                                                                                  
);

nginx/error.log:
empty

php/error.log

[20-Jan-2022 11:14:26] NOTICE: Terminating ...                                                                                                   
[20-Jan-2022 11:14:26] NOTICE: exiting, bye-bye!                                                                                                 
[20-Jan-2022 11:15:09] NOTICE: fpm is running, pid 403                                                                                           
[20-Jan-2022 11:15:09] NOTICE: ready to handle connections   

Permissions on log file:
-rw-r----- 1 abc abc 5110 Jan 19 23:00 nextcloud.log