Well this time it was instant. I just started up UE and made a new blank project, did “stat fps” and waved my mouse over the initially populated actor list in the scene outliner and it just started happening. Sometimes it doesn’t start until a few minutes in. Each time it’s inconsistent what I was doing beforehand. At first I thought maybe my system had an issue and the whole OS was halting. But I did some tests where I’d play a video or have something running beside UE that had an animation (like a flash video in a browser). I’d do the mouse over thing in UE to trigger the stutter, and UE would halt but nothing else on my system would. Everything else kept playing smoothly.