When I want to shutdown my PC I click the top right corner and then press the power button after which a dialog pops up with the options: power off, restart, cancel.
Normally this pop up shows up right away. But since a week or so it takes about 30 seconds. During that time I can move my mouse but I can't open applications or do anything else.
When I cancel and try it again, it does open right away.
I didn't change settings or install weird stuff, only some updates of my icon theme. (I apparently had installed the Caffeine extension).
What could be the cause? And how can I diagnose this issue and see what it taking so long?
There is a known bug in the Caffeine extension which causes GNOME shell to temporarily stop responding on first power button event. Disabling the extension should get rid of the issue.
As a replacement you may use another extension called Keep Awake! which provides similar (but with fewer options) functionality or wait (or hope) for the Caffeine extension to get updated with a fix.
Alternatively you may install the Caffeine application instead of the extension by running