Yesterday when doing an update via dnf, the xorg-x11-server-Xorg-1.19.6-1.fc27.x86_64 package was installed. Upon rebooting today, my display manager (lxdm) would not start, and the console terminal kept looping through tons of errors like this:
Process 753 (Xorg) of user 0 dumped core.
Stack trace of thread 753:
0x00007fc1f663b66b raise (
0x00007fc1f663d381 abort (
0x00000000005a046a OsAbort (Xorg)
0x0000000000479cac ddxGiveUp (Xorg)
0x00000000005a5f12 AbortServer (Xorg)
0x00000000005a6d55 FatalError (Xorg)
0x000000000059d55e OsSigHandler (Xorg)
0x00007fc1f69f9a80 __restore_rt (
0x00007fc1f663b66b raise (
0x00007fc1f663d381 abort (
0x00007fc1f66338fa __assert_fail_base (
0x00007fc1f6633972 __assert_fail (
0x0000000000421687 dixGetPrivateAddr.isra.3.part.4 (Xorg)
0x00000000004c4fbf compIsAlternateVisual (Xorg)
0x00007fc1f44aa877 __glXScreenInit (
0x00007fc1f44b17b6 __glXDRIscreenProbe (
0x00007fc1f44a9325 GlxExtensionInit (
0x00000000004a897d InitExtensions (Xorg)
0x000000000043971f dix_main (Xorg)
0x00007fc1f662500a __libc_start_main (
0x00000000004235fa _start (Xorg)

Stack trace of thread 766:
0x00007fc1f69f4c4b pthread_cond_wait@@GLIBC_2.3.2 (
0x00007fc1f11a63cb util_queue_thread_func (
0x00007fc1f11a62e7 impl_thrd_routine (
0x00007fc1f69ee61b start_thread (
0x00007fc1f671b91f __clone (

lxdm.service: Main process exited, code=exited, status=1/FAILURE
lxdm.service: Unit entered failed state.
lxdm.service: Failed with result 'exit-code'.
lxdm.service: Service hold-off time over, scheduling restart.
Luckily, I was able to switch to another terminal screen (despite the main console taking over every few seconds), and I then logged in as root and downgraded that package:
dnf downgrade xorg-x11-server-Xorg
Doing so took my F27 system back to the xorg-x11-server-Xorg-1.19.5-1.fc27.x86_64 package, and then after a few seconds lxdm started (without needing a reboot). All is well now. So downgrading the package fixed the problem.

Has anyone else here had any problems with that Xorg package update? It's possible that it might just be a problem for lxdm, so I'd be interested in hearing if other display managers have this problem with that Xorg update.