Recently I upgraded one of my VR projects to 4.16 and found out that UMG dragging with WidgetInteraction component is not working anymore. Previously (in 4.14, 4.15) I called PressPointerKey() and ReleasePointerKey() with EKeys::RightMouseButton to simulate dragging by right mouse. It worked well - scrollboxes, scrollbars and other draggable elements were dragging by interaction component. Now it’s broken. Please investigate this issue.
Ok. It’s a bug in WidgetInteractionComponent. And it’s already fixed in master branch of UE4 sources on GitHub. But looks like it’s targeted to 4.17. Anyway, it’s easy to fix on binary version of engine (from launcher) with making a copy of WidgetInteractionComponent with sources from 4.15. I hope this info will be helpful.