When we do the refactor for MeshDescription we miss the staticmesh reduction project settings option and change only the quadric reduction.
There are two possible fixes for this issue:
1. Implement simplygon MeshDescription reduction interface, which was not implemented since we want to deprecate simplygon
2. Remove the simplygon reduction option for staticmesh
See steps to reproduce in this thread: https://udn.unrealengine.com/questions/450982/unimplemented-simplygon-function-causes-empty-mesh.html
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-63621 in the post.