No login as admin possible

Suddenly I cant login as admin. Error message:

400 Bad request Incorrect Username or password

Username (admin) and password are correct (no typos). I can login with another username, I can use the services I have installed (FileBrowser and Photoprism) I can login into Paperless-NGX (docker installation via OMV). I can ssh on my Pi (username is not admin).

Browser cache cleared, tried another browser, but no luck.

No idea what else I can check.

Problem solved:
running omv-firstaid as root and resetting the failed login counter solved it.

Leads me to the question how many failed logins are possible and can this be changed?