Can't connect to self hosted server

For a few days now, I have been unable to log in to my self-hosted server on my network with my desktop app and the mobile app. I always get the error message “Failed to fetch”.

I also have a browser extension on the same computer as the desktop app, but this can connect and synchronize. I can also reach the server from any device at or https://bitwarden.lan without any problems, so it can’t be due to any network restrictions.

Server Installed
Server Latest
Web Installed
Web Latest

Does anyone else here have an idea what I can check?

Thanks in advance