Hey ZeJudge-
Are you referring to the mouse not updating while playing (in PIE or standalone) or when working in the editor viewport itself? What are you trying to drag around the level? In my tests I was able to add a new mesh / blueprint to the level and grad the transform arrows to move it around. If you don’t have anything selected when you hold the button, are you able to fly the viewport camera around (forward / backward as well as spin around)?