here's what happened:
I installed Ubuntu 19.10 without any problems but with automatic login enabled.
Then, I installed the software updates and rebooted my PC. After that, the system was asking me to type my password (he didn't to that before) and then I couldn't log into my account anymore, even though my password was right. (the famous login loop problem)
Finally I did found a solution (and was because the automatic login). I changed the file "/etc/gdm/custom.conf" (via Ctrl + Alt + F3 (Virtual Terminal)) and commented these lines:
AutomaticLoginEnable=True
AutomaticLogin=yourusername
After that, I rebooted my PC and everything worked fine.
Anyway, I just wanted to share it with you guys in case you didn't see this solution yet.
I don't know if it is a bug or something. (I guess it is)
I hope this helps someone out there.
Good luck and have a nice day.
