This post https://forums.unrealengine.com/unreal-engine/feedback-for-epic/1457519-4-19-4-20-editor-packaged-games-have-hangs-hiccups-constantly?p=1476112#post1476112 pretty much states it was reproducible and if you click on the issue you will see it was fixed.
We would need more details on your graphics card model and driver version to properly see if we can help reproducing… also a video of 1min duration with your experience would immensely help.