On a Dell Latitude 7490, some time after locking the screen (on Gnome), the
computer becomes unresponsive - some LEDs are still blinking, but there's no
way to get the screen to turn back on. (I haven't yet tried SSHing into the
machine in that state.) Note that this doesn't happen immediately - right after
locking the screen, the lock screen can still be unlocked. After waiting a bit,
sometimes it's in this unresponsive state.

The last messages before the (forced) reboot in /var/log/messages are as
follows:

2019-01-03T14:48:23.166843+01:00 linux-r9va dbus-daemon[1492]: [system]
Activating via systemd: service name='org.freedesktop.nm_dispatcher'
unit='dbus-org.freedesktop.nm-dispatcher.service' requested by ':1.7' (uid=0
pid=1722 comm="/usr/sbin/NetworkManager --no-daemon ")
2019-01-03T14:48:23.172078+01:00 linux-r9va systemd[1]: Starting Network
Manager Script Dispatcher Service...
2019-01-03T14:48:23.180329+01:00 linux-r9va dbus-daemon[1492]: [system]
Successfully activated service 'org.freedesktop.nm_dispatcher'
2019-01-03T14:48:23.181000+01:00 linux-r9va systemd[1]: Started Network Manager
Script Dispatcher Service.
2019-01-03T14:48:56.478390+01:00 linux-r9va gsd-media-keys[3259]: Couldn't lock
screen: Timeout was reached


This only started after or around Christmas, but it's happening a few times a
day now. My colleague Alexandros (in CC) is seeing a similar/the same problem
on the same hardware.

I'm reporting this against the kernel, because I got a kernel update on my
machine on Dec 21st, and I can't see any e.g. Gnome or Wayland packages updated
in that timeframe.