I’m running the PureOS 8 beta on my librem 15. About 1-2 weeks ago, I noticed that when the screen saver started my X session would terminate half of the time. I decided to disable sleep, while I was connected to power. This worked fairly well for a few days. Today I applied an update, via the gnome updater. Since that update, about 30 minutes ago, I’ve been logged out twice. Once was during an initial login. The other time, I was switching desktops. The most confounding bit, in all of this, is my tmux sessions are lost, when I’m logged out.
The first logout coincided with a segfault from Xwayland. The second did not. I followed the steps outlined here. It did not report anything changed.
I did find that some others were having issues with segfaults in gnome 3.27 and 3.28. I’ve lost the links tho. 
[Fri Jun 8 16:17:38 2018] rfkill: input handler disabled
[Fri Jun 8 16:17:42 2018] gnome-shell[1635]: segfault at 1a0016 ip 00007fdf3fad0d3d sp 00007ffe9456dc80 error 4 in libgobject-2.0.so.0.5600.1[7fdf3fa9b000+52000]
[Fri Jun 8 16:17:43 2018] audit: type=1400 audit(1528489062.816:77): apparmor="STATUS" operation="profile_load" profile="unconfined" name="docker-default" pid=2529 comm="apparmor_parser"
[Fri Jun 8 16:17:43 2018] bridge: filtering via arp/ip/ip6tables is no longer available by default. Update your scripts to load br_netfilter if you need this.
[Fri Jun 8 16:17:43 2018] Bridge firewalling registered
[Fri Jun 8 16:17:43 2018] Initializing XFRM netlink socket
[Fri Jun 8 16:17:43 2018] IPv6: ADDRCONF(NETDEV_UP): docker0: link is not ready
[Fri Jun 8 16:17:44 2018] rfkill: input handler enabled
[Fri Jun 8 16:17:53 2018] rfkill: input handler disabled
[Fri Jun 8 16:18:03 2018] tun: Universal TUN/TAP device driver, 1.6
[Fri Jun 8 16:24:19 2018] rfkill: input handler enabled
[Fri Jun 8 16:24:34 2018] rfkill: input handler disabled