Widget interaction lag issues I am not familiar with, can be many reasons also generallly the WidgetComponent is heavy in terms of rending so better check the ui render times, ui stat also you can use widget reflector to see what is happening. If its rendering lag etc you can use manual painting on mouse move.
On this question you ask not sure but as i understand you are making a custom hit test to widget. Which is totally fine and you can manually access widgets like that aswell, however better use camera forward or relative vector to hit test so movement doesn’t effects it or rotations.
On my example when I am doing a line trace in world to detect widgets world locations, i use mouse pos so its from near camera to the direction of mouse so it doesn’t get effected from turns.