This is the correct behaviour. LightDM hasn't crashed, it has just exited with an error code (you can see this in /var/log/lightdm/lightdm.log). Ubuntu then shows you a failsafe mode to prompt you to fix your system.
I'll reassign this to xdiagnose which is the failsafe mode you are seeing - it would be nice if it could provide more accurate information on what has happened.
This is the correct behaviour. LightDM hasn't crashed, it has just exited with an error code (you can see this in /var/log/ lightdm/ lightdm. log). Ubuntu then shows you a failsafe mode to prompt you to fix your system.
I'll reassign this to xdiagnose which is the failsafe mode you are seeing - it would be nice if it could provide more accurate information on what has happened.