Re-posting here for future Google searches.
See attached for my solution.
This was driving me crazy, and I zero’d in that it was somehow being caused by the PostProcessVolume in the level. Disabling it entirely would remove the super fast VFX/blueprints, but then the lighting wouldn’t look right. Tweaking the Blend Weight of the post-process volume ALSO made it stop, but only with values below a certain threshold, ~.82.
After some thought, and remembering that what’s in-game vs MRQ can be very inconsistent and weird sometimes, I tried just adding the Motion Blur Amount to the camera that was being rendered.
Problem gone!
