I’m experiencing the exact same issue. I’m working on it now and will let you know if I find an answer. From what I’ve read elsewhere it seems that capturing and displaying dynamic shadows may be the culprit. Temporal AA also seemed to have caused screen flicker pre 4.13 in a packaged game when scene capture was displayed but that might not have an effect on framerate or be an issue if you are using 4.13+. I haven’t updated from 4.11 since that is what was current when I started making my game and I’m frankly afraid to update considering the issues that transferring a game in progress between updates can cause.