Suddenly, I cannot login to the Web Control Panel. (At the same time ssh is no problem.)
Credentials are correct (I am using Lastpass to auto fill the form fields). To be sure I have double checked and tried it manually as well.
The Login seems to work (no errors) but after a few seconds the Login screen is shown again. It is in a loop.
FYI: When I intentionally use a wrong password I get the usual red error message
What I've tried to fix it:
3 Change control panel administrator password
4 Reset failed login attampts
apt-get update && apt-get upgrade
What I suspect caused it:
The last time I was logged into the web panel I was using the "Update Manager".
I think the "upgrade" did not work. Unfortunately I can't recall the details.
After that the problem happened.
When I do this via ssh I get the following: