UWidgetComponent is still experimental, the document said that the input handling is still not perfect (please correct me if i’m wrong, i think i’ve read it somewhere in the document).
And I see that you’re using 4.9, if the problem is with the mouse input, there’s a bug in UMG’s widgetcomponent where the mouse cursor location are transform incorrectly to the widget. You can fix this by setting UWidgetComponent::bUseLegacyRotation to true (the default is false). I don’t know if this bug has been fixed or not in the later version (4.11) or not