Apps may hang when switching between them.
For example, here is the case, which 100% hangs the drawing.
1) Open YouTube app
2) Start playing a video
3) Open another app
4) It second app hangs.
5) Go back to first app - it is also hanged.
Most probably, it happens because we don't honor Active, Inactive, Visible, Invisible and other events from libwindowmanager. Going to implement them and see if something happens.