In Fedora 37, KDE now regularly freezes whenever the display configuration is implicitly changed, for example by connecting an external monitor or closing the laptop lid (thereby turning off the second screen). And every couple of days, it even freezes without any display change.

I've used KDE on Fedora for years with multiple monitors, for example on a docking station, often removing the laptop from the docking station disconnecting the additional monitors and back. Although there were bugs, it worked fine most of the time but now, it appears to have become terribly buggy and unreliable on Fedora 37.

Symptoms:
The taskbar freezes, so the clock is stuck and when switching workspaces, the taskbar still shows the windows from the previous workspace. However, everything else seems to work normally, it is possible to use the system as long as you remember which windows you have open and on which workspace (or use Alt+Tab to see a list, that works too). If you're connected to the wrong network or want to change the volume, you're out of luck because those settings are controlled from the KDE taskbar which is frozen.

Workaround:
Either open a terminal from within KDE or hit Ctrl+Alt+F3 to switch to a text tty, log in and enter:
export DISPLAY=:0
Run this command to terminate and restart the frozen KDE panel:
pkill plasmashell ; plasmashell --replace &
(If you've switched to a test tty, hit Ctrl+Alt+F2 or similar to go back to your graphical desktop.)

Symptom:
Another aspect is that, when turning off a monitor, the lock screen is broken. You'd go away for a couple of minutes or lock manually, come back to your laptop and instead of the lock screen with the password prompt and everything, you get a blue screen (not a Windows bluescreen), as if the second monitor that you've disconnected was still there and is now showing the password prompt as if KDE didn't notice that that monitor is gone. (In a multi-monitor setup, KDE will show the password prompt on one screen only and it appears to be the one which happens to have the mouse cursor on it.)

Workaround:
To get back into your KDE session when the lock screen does not show a password prompt after changing monitors, you need to terminate the lock screen manually from a text tty:
1. Switch to a text tty: Ctrl+Alt+F3, log in and run this command once:
export DISPLAY=:0
2. Enter this command to terminate the frozen lock screen:
pkill -9 kscreenlocker
3. Switch back to your graphical desktop: Ctrl+Alt+F2



Reproducible: Always

Steps to Reproduce:
1. Open bug report for Fedora.
2. Wait.
3. Bug report is closed automatically with "CLOSED EOL".
Actual Results:  
It seems like KDE does not notice when a monitor is turned off.

Expected Results:  
You'd think a desktop environment suite as mature and old as KDE would be able to handle multiple monitors even when one of them is turned off without restarting the computer.

I consider using KDE on a multi-monitor workstation a major feature, so I'm setting the severity accordingly.

I've not yet seen relevant log messages when this happens. But I've noticed that the following new log message is filling the system log:

deepin-system-monitor-plugin-popup[3481101]: QDBusArgument: read from a write-only object

It seems to run some kind of infinite loop:
# grep -c 'deepin-system-monitor-plugin-popup' /var/log/messages
171103

I don't know what this is. It's obviously broken, so I want to get rid of it. Don't know if that's related to KDE freezing almost daily now.