Thanks for performing those tests. It definitely appears that there is an issue with that particular map.
- Could you please provide your dxdiag?
- Could you please zip up the .umap file and provide it? You can PM it to me on the forums if you’re concerned about privacy: https://forums.unrealengine.com/member.php?160394-Sean-Flint
- Have you tried recreating the map from scratch to see if you experience the same results after a certain point?