Multiple licensees are experiencing this problem. The repro should look like this initially:
But then over time will degrade overtime into something like this this, most likely caused by a PSO caching + shader mismatch error:
1. Download 4.21 project repro provided by licensee - [Link Removed]
2. Deploy to XboxOne on 180604 / October 2018
3. Y is set to "Seamless Server Travel", forcing the the level to reload.
4. Keep pressing Y until artifacts begin to appear (usually around 10-20 presses, frequency seems to increase).
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-67143 in the post.