Then you must have broken something in your user folder. Permissions are a possible problem.
I have never seen this file requested before, and is actually not existent:
thunar-WARNING **: 21:30:52.216: Content type loading failed for .Xauthority-c: Error when getting information for file “/home/user/.Xauthority-c”: No such file or directory
This cries out “Permission problem”:
Authorization required, but no authorization protocol specified
Check your group(s) and repair user folder permissions, if needed.
You might use this command:
id
Did you have any crashes, or unwanted power off, just before these happen?
I was obviously blind or my mind played tricks… .Xauthority is owned by root.
Delete .Xauthority (you may need to login TTY with root user) and login with LightDM as usual.
Just don’t try to login to your user account from TTY with sudo again.
Tip: Always confirm your current directory contents with ls -a, before doing important actions.