Well, I encountered this strange bug, and after 6 hours trying to figure it out, I found a solution. Whenever you enter a level, execute the following command in the console:
r.OneFrameThreadLag 0.
If that doesn’t work, try these commands:
r.VSync 1,
r.NumBufferedFrames 1,
t.MaxFPS 90 (or whatever number you prefer),
and run stat unit twice.
I’m not exactly sure how this works, but it worked for me, and I hope it helps you or anyone else who finds this.