I restarted my computer and was presented with the following error message upon gdm3 start:
Could not update ICEauthority file in /var/lib/gdm3/.ICEauthority
* What led up to the situation?
I just restarted the computer.
* What exactly did you do (or not do) that was effective (or
ineffective)?
I tried to move the file and create a blank one. This didn't help.
Then I found a .ICEauthority file in my home directory. I moved this and the error message on bootup was gone.
Thus I suspect the error message was about the file in /home/user/.ICEauthority instead of /var/lib/gdm3.