Comment # 1 on bug 1084798 from Michal Srb

Do you use vncserver by any chance? (There is existing issue where xauth
started by vncserver overwrites existing Xauthority entries.)

When the issue happens, please collect and attach the output of following
commands:
* echo $DISPLAY
* echo $XAUTHORITY
* echo $XAUTHLOCALHOSTNAME
* hostname
* xauth list

Note that the advice about "video" group from the forum is wrong. This is about
authentication between X application and X server, "video" group has nothing to
do with it.