Comment #52 makes me think it's Xwayland that went away. But NOT related to any log messages mentioning "Xwayland" because those are just from the login screen and harmless. It looks like the lock screen may have caused the login's Xwayland instance to crash silently or just exit, which is why a bunch of binaries start failing and one explicitly mentions ":0" (the connection to Xwayland).
Comment #51 is bug 2034665.
Comment #52 makes me think it's Xwayland that went away. But NOT related to any log messages mentioning "Xwayland" because those are just from the login screen and harmless. It looks like the lock screen may have caused the login's Xwayland instance to crash silently or just exit, which is why a bunch of binaries start failing and one explicitly mentions ":0" (the connection to Xwayland).