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 ideass on how can I fix, or further troubleshoot this?

GNOME Shell 3.36.2

  • 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 '20 at 9:32
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    killall works! Thank you so much! – darw Nov 10 '20 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. – Nicholas DiPiazza Dec 12 '20 at 4:33
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    You can also restart gnome via Alt+F2 -> type "r" -> Enter -> Boom. Seems like a Gnome bug. – Íhor Mé Feb 20 at 9:55

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.

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