Stuck Login screen until reloading website and error

Nextcloud version (eg, 18.0.2):
Operating system and version (eg, Ubuntu 20.04): Debian 1

The issue you are facing: When I want to login, the site doesnt continue. I need to reload the website, so I can get logged in (after typing in the password etc.)
Another issue: I cant delete files through Nextcloud. I can only delete them via FTP. The error: “file couldnt be deleted”
Another small issue: The site needs really long to load. But this could also be the reason of my server.

Is this the first time you’ve seen this error? (Y/N): No I have this since the first installation

The output of your Nextcloud log in Admin > Logging:

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

For the first problem: I also have a similar problem with the software “Jellyfin”. Everytime I add a song to a playlist I need to reload the page