Cannot login - invalid token

I cannot log in to Matomo anymore, I get the following error message:

Fehler : Formularsicherheit fehlgeschlagen, Token stimmt nicht überein. Bitte laden Sie das Formular neu und überprüfen Sie, ob Ihre Cookies aktiviert sind.

Which means: Security Issue, invalid token. Reload form and activate cookies. I post here because there was no response in the German forum. This happens in different browsers, Cookies are active, it first happened four weeks ago and since then I cannot log in anymore. Any suggestions?

Thanks, Daniel

Did you try in private mode?