To reproduce, there are 2 ways:
1. Open new project.
2. Open SceneView
3. Create Empty game object.
4. Add "Cloth" component to it.
5. In "SkinnedMeshRenerer" select any mesh.
6. Undo this action.

OR

1. Open new project.
2. Open GameView.
3. Create Empty object.
4. Add "Cloth" component to it.
5. In "SkinnedMeshRenderer" select any mesh.
6. Undo this action. (no crash yet)
7. Open SceneView.
8. In "SkinnedMeshRenderer" open Mesh selection. - CRASH

Expected result: no crash
Actual result: crashes at SkinnedMeshRenderer::UpdateVertexBuffer

Notes: Cloth component is needed for this crash.

Reproducible: 5.6.0a1, 5.6.0b7
Not reproducible: 5.5.1f1 (or any other 5.5)