Bug#890517: killer's CRON logs out users once per hour
> We never came to the point to investigate this closer, but personally,
> I think that killer on a Debian Edu system with MATE desktop env has
> not been usable at least since jessie.
The only way I can think of that this can happen, is if the display
manager is broken and fail to register logged in users in the utmp/wtmp
files. You can verify this by running 'w' or 'who' after login to see
if the user is registered as logged in. If this is the case, the fatal
bug is in the login service you are using, not killer.