"Login failed" after 5-10min


i’m using nextcloud on my local NUC-Server with Ubuntu, docker and reverse proxy.
Since tomorrow morning logins from my personal account fail after about 5-10mins. So i login or generate a new app-password and after 5-10mins this login doesn’t work anymore an logfiles tell me “Login faild”.

This means other logins have no problems. But my account is not working. Generated App Passwords as long as manual Logins. The problem is present on native Windows- and Android-Clients as long as on several WebDAV-Clients.

The Logfile is not really helpfull. It just logs a positive Login and after a while failed logins.
Has anyone an idea where to search for the issue.
I read anything about “configure apache2” but i’m not clear if this would help on a docker-installation.

Thanks for help,