Complete desktop lock-up at random

I tried to bring up the debug menu (with the Backspace key) which caused the entire desktop to lock up: the mouse did nothing, the keyboard did nothing, and even pressing capslock or numlock didn't toggle the lights on my keyboard, nor did attempting to switch to a virtual terminal do anything; I had to do a hard power off.  Also, the background music "skipped", replaying the same one second of sound over and over.

Neither the system log nor xsession-errors showed anything useful.

Attached are the output of dmidecode and glxinfo

System info:

• Fedora 28
• Kernel 4.17.6
• X server 1.19.6
• Lenovo H50-55 desktop
• AMD A8-7600 Radeon R7, 10 Compute Cores 4C+6G
• Steam was started in a Flatpak container

EDIT: Also, the game was in windowed mode when this happened.

EDIT 2: This also happened while loading a saved game, before the load finished, so it happens completely at random.  I tried loading the same game over and over to duplicate, but it seems to happen completely at random.

Might be related to Steam linux client issue #5334

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Attachments:

glxinfo.txt

dmidecode.txt