Actually this problems frustrated me for years since I start to use krita, it just not respond to mouse scroll/middle click to zoom/pan canvas, but it works on other parts(UI…).
This happens sometimes when I jump off the app then switch back, but it not always appeared, sometimes bugs come when I just save image. And I cannot fix it unless I restart the program(sometimes even this wont fix it, I must relogin). I found other reports this issues either(seems it exists for years), but non of these simple fix works for me( reinstall drivers/krita, click sidebar, click window bar etc…).
And today I decide to research it seriously.
I enabled the tablet logging and the log viewer, I see these things below
As you can see, seems the canvas is focused and it reads the mouse middle button(button 4) and the scroll event, but just not pan and zoom(zoom works on ctrl+/- and the zoom scrollbar on bottom). That’s really weird