Some App Instances cannot be focused

Solution 1:

So, I don't know if this will work always, but I found one workaround:

  1. Switch to the non-showing instance of the app.
  2. Switch to another instance of the app that shows.
  3. Put this app in full screen
  4. Switch to the non-showing instance of the app -> now it worked for me.

I am not sure if 1-3 have to happen on the same monitor, I will keep trying this out in the next days...