I’m confirming that! That strange behaviour happened to me after upgrading from 4.19.2 to 4.20.3.
‘Event On Mouse Enter’ in my widget has been firing when mouse cursor was just hovering over widget.
I had ‘Use Mouse for Touch’ = true in Project Settings, and Show Mouse Cursor, Enable Touch Events, Enable Touch Over Events all set to true in PlayerController.
After setting Show Mouse Cursor to false and set Default Cursor to None (!! which was especially weird), ‘Event On Mouse Enter’ in my widget stop fire on mouse hovering.
Also I managed to solve that problem in another way: I’m checking if Mouse Event is touch, because it looks like that event is firing one time for Touch plus one time for Mouse, but only with visible(?) mouse cursor.