There is requested video. Captured from iPad pro using QuickTime Player.
https://dl.dropboxusercontent.com/mov
Bug is only visible on iOS. Using Metal preview on Mac Editor does not yield same bug.
I really appreciate your patience while we determined the validity of this bug. I have gone ahead and entered a report for the issue, UE-32289. What we suspect is happening is that it’s a UV or Z precision issue unique to iOS Metal.
Once the issue has been addressed by our engineers, the fix will be added to the release notes for fixed issues within an upcoming full engine or hotfix release.
Let me know if you have further questions or need additional assistance.
I guess it’s either wrong uv’s for landscape ligthmaps or wrong lightmap binding.