This is not a regression,repro in 4.21
1) ** Open scene scene attached in 3Ds Max.
2) View simple Window. Open Material editor
3) Using the Eye dropper , Click on the windows.
4) Notice this is a Multi-Sub Corona Material ( see image)
5) Go to file export using Datasmith
6) Open Unreal
7) Import Scene
--> Notice that the Windows have a strange look , UVs are all messed up.
8) Click on window static mesh
9) Click on Mesh Editing tab
--> Notice the Mesh correct itself .
10) Close Window , Notice that the windows Issue in the viewer is now fixed....
--> Link for file here :[Link Removed]
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-69233 in the post.