When it’s giving you this problem, what does your Task Manager==>Performance page look like(cpu/gpu/mem/hdd)? What do your temperatures look like(could be thermal throttling? Are you running out of ram? If you are, then it could be stutter coming from HDD thrashing the page file. Are you simulating the viewport, if so, could it possibly be some bad blueprint of yours that has a glitchy loop in it?
This would be one of those test questions where the answer would be D) Not enough information.