Video of it NOT working in Unrela 4.18: Unreal 4.18 UI Animation Problem - YouTube
Happy to show code if you have any idea - or - can give me confirmation if this is a BUG that would also be helpful. Thanks!
SOLVED: The problem may have been caused by the way the Widget interacted with the collision-box! I set custom Collision to overlap PAWN only on the collision box inside the 3D Widget.