Hello, So I stumbled upon this issue just now and my Krita version is 5.1.5. I am here to share my experienced and the possible fix that my work to some people who experienced this issue.
So I followed KnowZero “Log Viewer Docker” and because I have a little but not so great knowledge about programming I noticed that the logs says that the F3 and F4 is being pressed despite me not pressing it. Hence, I came to conclusion that this pressed keys are interfering with the “Ctrl + Space” or other Key Combos
What I did to “fix” this is I pressed the mentioned keys which are F3 and F4, as you can see at the image, at the second warning line it didn’t mention F3 as because I click it then once I realized that it really work I tried it to F4. after doing this simple step I manage to use the Key Combo again
I noticed that this issue happens whenever I switch tabs but I can’t recreate the issue to be sure about that. But anyway, hope this helps whoever sees this that experiencing same problem to me.