I managed to get it on kernel 5.15 and replicate the issue. I had to find its USB-C charger to keep it on while I power down my monitor otherwise it would hard shutdown it. So, connecting the monitor back, the weirdest thing just happened. The display rearranged, but didn’t use the new monitor. Instead, the lock screen got resized and I could see my session behind it without logging in (!).
I’ve got this on dmesg: [119330.829398] amdgpu 0000:63:00.0: [drm] *ERROR* no VCPI for [MST PORT:00000000e7b3da3d] found in mst state 000000005563f49a
journalctl gives more details:
<span style="color:#323232;">May 03 17:05:01 Glass /usr/libexec/gdm-x-session[1601]: (II) AMDGPU(0): Allocate new frame buffer 2560x1440
</span><span style="color:#323232;">May 03 17:05:01 Glass /usr/libexec/gdm-x-session[1601]: (II) AMDGPU(0): => pitch 10240 bytes
</span><span style="color:#323232;">May 03 17:05:01 Glass rtkit-daemon[1209]: Supervising 7 threads of 3 processes of 1 users.
</span><span style="color:#323232;">May 03 17:05:01 Glass rtkit-daemon[1209]: Successfully made thread 33483 of process 1581 owned by '1000' RT at priority 5.
</span><span style="color:#323232;">May 03 17:05:01 Glass rtkit-daemon[1209]: Supervising 8 threads of 3 processes of 1 users.
</span><span style="color:#323232;">May 03 17:05:01 Glass csd-media-keys[1761]: Unable to get default sink
</span><span style="color:#323232;">May 03 17:05:01 Glass csd-color[1770]: failed to reset xrandr-Samsung Electric Company-SAMSUNG gamma tables: gamma size is zero
</span><span style="color:#323232;">May 03 17:05:01 Glass csd-color[1770]: failed to reset xrandr-Samsung Electric Company-SAMSUNG gamma tables: gamma size is zero
</span><span style="color:#323232;">May 03 17:05:01 Glass /usr/libexec/gdm-x-session[1601]: (II) Quirked EDID physical size to 0x0 cm
</span><span style="color:#323232;">May 03 17:05:01 Glass /usr/libexec/gdm-x-session[1601]: (--) AMDGPU(0): HDMI max TMDS frequency 225000KHz
</span><span style="color:#323232;">May 03 17:05:01 Glass /usr/libexec/gdm-x-session[1601]: (II) AMDGPU(0): EDID vendor "SAM", prod id 29044
</span><span style="color:#323232;">May 03 17:05:01 Glass /usr/libexec/gdm-x-session[1601]: (II) AMDGPU(0): Using hsync ranges from config file
</span><span style="color:#323232;">May 03 17:05:01 Glass /usr/libexec/gdm-x-session[1601]: (II) AMDGPU(0): Using vrefresh ranges from config file
</span><span style="color:#323232;">May 03 17:05:01 Glass /usr/libexec/gdm-x-session[1601]: (II) AMDGPU(0): Printing DDC gathered Modelines:
</span>
I got it to switch monitors using Cinammon’s Display app, but it will not take two displays at the same time.