Bug 472049

Created attachment 160124 [details]
Backtrace generated using gdb (never used it before - please let me know if more info is required and I'll do my best to provide).

SUMMARY
***
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***


STEPS TO REPRODUCE
1. Attach a new monitor to a device with a built-in monitor; OR, wake up the device from suspend state that has a second monitor connected
2. Sometimes plasmashell dies (see next section)

OBSERVED RESULT
Plasmashell is "dead", the only thing that's visible is a black screen with a cursor, which can be moved between 2 screens. Alt-tabbing between applications or using other keyboard shortcuts doesn't work. If Bluetooth headphones are paired, they'll make a sound as if they connected to the device successfully. Any open applications will stay open and "alive", but in this state they cannot be interacted with.
If this happens during waking up from sleep, then the login screen will be visible for a short moment before going black as described above. That only happens with Plasma login screen, and not when logging into from SDDM.
This bug is not observed every time and I don't know what exactly to do to faultlessly reproduce it. It just happens sometimes.

EXPECTED RESULT
The second monitor connects as usual, or the device wakes up as usual. KDE works normally.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux , kernel 6.4.1-arch1-1 (64-bit)
(available in About System)
KDE Plasma Version: 5.27.6 
KDE Frameworks Version: 5.107.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION
Graphics platform: X11
I went Wayland for a couple days and this bug haven't happened once then, but it was only a couple days, so I'm not sure if Wayland fixed it or I was just lucky.. On the other hand, on X11 it usually happens at least once a day, so...
Graphics drivers: AMDGPU (open-source)
Refresh rate of both built-in and secondary monitors is 60 Hz. They are connected via a HDMI-HDMI cable.
Another note: sometimes Spectacle crashes too. I mention it here because the conditions for it crashing are identical, but I can't create a separate bug report yet because I haven't had time to properly gather information for that.