Ue4, Crashes WhenReimport Skeletal Mesh

Im Using 4.15.3

My Editor Crashes When i Reimport my Skeletal Mesh, No there are no Really Changes, the Only Change is that i Updated my UE, From 4.15.2 to 4.15.3 .
When i DELETE all my Materials!, So whitout MaterialTag, it Works,But with Material It crashes Instantly.

When i Import the Skeletal Mesh Fresh as a New one in a Other Folder it Works like a Charm
And no i Dont wanna Import it as A Fesh one, and than Retaget all Anim BP’s, because i have a Lot stuff Connected with it.

Any Ideas?

Using C4D for Main Appl.