Comment 23 for bug 1978398

I had the same error and it was hanging on startup.

To fix the issue, I pressed ctrl + alt + F2 to switch to TTY2. Logged in there and ran `sudo apt update` and `sudo apt upgrade`.

I'm afraid I didn't pay too much attention since I didn't expect it to work, but it looks like something related to nvidia drivers were not fully installed. On reboot I get a brief look at possibly the same message, but it no longer hangs on start up. I suspect at least some of the other users are in the same boat as me.