I have designed my scene and everything was working fine including navmesh and character movement.
Since 2 days , when i rebake the scene , navmesh (the blue area) doesn’t show up .
plus I cant move or resize any of my gameobject in scene !!! Only the wire frame will move or resize ?
please see the attached image for a clear screenshot of the problem.
The mesh filter says “Combined Mesh”…
It’s look like that you’ve bake all of the mesh include that rock’s mesh using somekind of mesh baker(plug ins maybe, or idk, maybe the new unity has one). Maybe you should unbake or disable the mesh combiner first…
That wireframe belongs to the mesh collider cmiiw…
Thanks a lot bart ,I think that should be the problem , But now how do i "decombine " my meshes ? .While developing the apk file ,I have checked 'static batching ’ and dynamic batching in player setting. Will this be the issue , but I tried disabling it , still the problem persist 
Unity does combine static meshes if you have Static batching active.
But this will only happen on playing the scene and not during the edit time.
In your case it looks like you have replaced your scene objects with a copy of the runtime(Combined) object.
In case you did not copy a object while playing and pasting it back when the play mode is ended its a big bug.
To repair you broken mehres you have to select the correct mesh to render on every object again.
For your rock example you select in your meshfilter the mesh rock_042 .(you can see the name in the mesh collider)
As you have mentioned , I didnot copy a object while playing and pasting it back when the playmode ended. so i guess its a bug. anyways thank a lot 
