I also feel like I’m getting random spikes where it should not be happening. Interesting that the runningstart command seems to be making a difference but obviously not very viable if we can’t force that from UE to a user. Have you tried messing with OpenXR to see if that solves things? I was thinking about switching but I can’t easily migrate my current project to do an accurate comparison.
EDIT: Or UE4.27 / UE5 for that matter. Feels like they’re all built on 4.26 so not sure if it would help but who knows.