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Meshes that animate via vertex deformations using worldposition offset display incorrect surface normals while animating. The reflections of the environment smear as the mesh moves making it look translucent or otherwise incorrect. The expected result gif was taken from 4.13 binary. The broken gif was taken in 4.19.
Follow this guild and finally I can't get correct surface Normals when the geometry vertexes are animating
For simplified things, you can just go to StaticMesh'/Engine/Functions/Engine_MaterialFunctions02/ExampleContent/TextureBasedWPO/DemoBoxMesh.DemoBoxMesh'
This is a TexturebasedMorph demo we provided, it looks also has incorrect normals
Observe that the surface of the mesh displays inaccurate, smearing reflections when animating with world position offset
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-53957 in the post.