When I try to open PhysicsAsset UnrealEditer crashes

Icreated character model with bone, and imported UE4(4.21), It was possible to opnen PhysicsAsset at first. I closed viewport and closed PhysicsAsset window.
After this I tried to open PhysicsAsset again and again but it could not.
maybe closing viesport of PhysicsAsset cause this crashes.
it can export everytime. Skeltalmesh and Skelton has no problem, it can open those window and edit. but Itried open PhysicsAsset, the window "start up UnrealEditor…"and close UnrealEditor display UnrealEngine crash reporter Irepeat same operation in 4.20 itworked but after closing viewport,Unrealeditor crashed. Other character model same.

I solved this problem.
My expected reason is true, closing viewport in PhysicsAsset window cause crashes.
If you have same situation, try “window” in your project→"reset rayout" and restart UnrealEditor.
It enable you to open the PhysicsAsset window, but your costmizesed rayout also reset.