Mine are all to do with how multimonitor is still a half finished mess:
Direct audio to the monitor that the app is placed on automatically.
Better handling of different monitor sizes so that the mouse ends up in the right place when moving between a 27 and a small one that are both 1080.
Bezel correction that doesnt result in a gap that the mouse cannot traverse.
Fix extreme corners of screens not moving to the other monitor, needing to me moved down about half a titlebar width to get across.
Fix the snapping to the sides of screens thing jamming up being able to move apps between screens needing it to be turned off, also disabling the windows+arrow combinations to move windows.