when in a user's home directory a .Xauthority file exists that is owned
by root (which for example happens when trying to debug a non-starting x
server with sudo startx or from buggy desktop managers), lightdm's user
sessions terminate without indication of what is wrong (no mention of
Xauthority in any log file).

in comparison, startx gives a debug message about not being able to
write to .Xauthority, and xdm seems to unlink the .Xauthority file.

both behaviors would be viable solutions in my opinion, but the current
form of silent failure is hard to debug; please consider easing that
either way.

thank you
chrysn