Kubuntu screen freeze when alt+tab

[itsme223]

Hi, I have kubuntu 22.04 installed and sometimes when I alt-tab it freezes the screen. The mouse is still moving and still interacts (can hear video audio stopping and starting) but the screen is frozen. I can ctrl-alt-f2 and restart sddm but would like to stop the problem.

[Schwarzer Kater]

Have you checked any log files and looked for entries at the time when the " [alt]-[tab]-freeze " happens?

For example see https://www.cyberciti.biz/faq/linux-...ew-logs-files/ or use something like KSystemLog.

[itsme223]

Thanks for the reply. I cant see anything obvious in the logs, is there anything in particular I should be looking for?

[Schwarzer Kater]

Could have something to do with KWin for example.
I found https://bugs.kde.org/show_bug.cgi?id=460455 doing just a quick internet search, but there were more results…

Which KDE Plasma and Frameworks versions do you use?

[itsme223]

KDE Plasma Version 5.24.7
KDE Frameworks Version 5.95.0
Kernel Version 5.15.0-6
Graphics Platform: X11

I have tried to reinstall but the problem is still there

[Schwarzer Kater]

If you have already taken measures like reinstalling the system… - does this " [alt]-[tab]-freeze " also occur when you boot the computer into a live environment from an USB stick?

[GreyGeek]

KDE Plasma 5.27 is out. You should upgrade to it and see if it fixes the problem. Otherwise: System Settings > Window Management > Task Switcher and try something else other than Breeze. Perhaps Compact?
Perhaps using Wayland instead of X11?

[itsme223]

I booted into a live environment and alt-tab for 5 mins and nothing happened. I saw changing the task switcher might help from another post but it didn't fix it. I'll try installing KDE Plasma 5.27

[Schwarzer Kater]

KDE Plasma 5.27 is out. You should upgrade to it and see if it fixes the problem.[…]

Not officially possible with Kubuntu 22.04 at the moment, afaik…
But you could enable the Kubuntu Backports :

sudo add-apt-repository ppa:kubuntu-ppa/backports
sudo update
sudo full-upgrade

and see if Frameworks 5.98 somehow fixes your problem (if it still occurs when booting Kubuntu 22.04 from a live USB stick…).

[itsme223]

I tried installing KDE Plasma 5.27 but didn't work. Would switching to Kubuntu 22.10 have a chance of fixing it?

[GreyGeek]

I tried installing KDE Plasma 5.27 but didn't work. Would switching to Kubuntu 22.10 have a chance of fixing it?

We're working blind here. You say you booted a Live USB and didn't have a problem. What distro and version?
What is the make and model of your computer, and its video chip?
BTW, did you try setting Wayland as your DM?

[itsme223]

the USB boot was kubuntu 22.04 same as full install.
PC spec:
CPU: AMD 1800x
GPU: AMD RX480
RAM: 24GB

I'll try Wayland now

[itsme223]

switching Wayland has to solve it. Thanks for your help

[arsivci]

This happened to me twice with stock 22.04.1, fully updated, X11. Could not pursue it because it happened a few days apart and I failed to reproduce it. Switcher theme was Kubuntu or informative; can't remember. In both cases Firefox and a few spreadsheets (LO) were open. At first, I put the blame on FF because my action was not smooth: alt (FF disclosed its menu) + tab. So, I changed FF to show its menu at all times and forgot about it. It happened again a few days later, however. Mouse was moving but not functional. Managed to drop to a tty but failed to start X. I did not have time to investigate further as I was in a hurry.