I recently updated to 20.04 LTS from 18.04 LTS.
When my system is up for like a day, alt-tab starts to lag. Not the window switcher panel, but when I select the window I want and release keys, it takes maybe a second to switch.

Rebooting or restarting gnome with killall -SIGQUIT gnome-shell fixes it back.
I also noticed gnome-shell was constantly at ~10% CPU while after restart, it's ~3%. Not sure if related.

I couldn't find anything about this problem. Any ideas on how can I fix, or further troubleshoot this?

GNOME Shell 3.36.2<br>
  • I have the same issue, I believe it might be related to the nvidia drivers. Currently downgrading to 390 to see if that helps
    – BenSower
    Oct 6, 2020 at 9:32
  • 2
    killall works! Thank you so much!
    – darw
    Nov 10, 2020 at 15:48
  • I don't have nvdia and I also have this issue. I'm on Radeon vega graphics AMD chip. by the way thanks for the killall trick. you saving my life. I am not using the proprietary drivers in my case. i will install them and see what happens. Dec 12, 2020 at 4:33
  • 4
    You can also restart gnome via Alt+F2 -> type "r" -> Enter -> Boom. Seems like a Gnome bug.
    – Íhor Mé
    Feb 20, 2021 at 9:55

2 Answers 2


I just had the same issue after migrating from 18.04 to 20.04, but I am using lightdm. Downgrading the nvidia-driver to 390 and restarting my machine solved the issue.

You can follow this link on how to update your drivers, but instead of the newest, choose an older one.

I only tried 390 so far, but a newer version might work as well.


In Ubuntu Mate, unchecking Windows->Show thumbnails in Alt-tab saved me for now.

I prefer not viewing Thumbnails than having all this lag.


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