I was having same problem on my VR game. When I checked “Used Fixed Frame Rate” it would work. I could tell because the frame rate on my motion controllers stayed down at the set amount. Then if I closed and re opened Unreal everything physics would be running twice as fast and justering and my motion controllers would be back up at a super high FPS and juttering randomly. I checked the config file and everything looked good there. I got a work around by putting a console command on the level start
t.MaxFPS=50
Or what ever frame rate you are trying for.
Hope that helps 