Unity Oculus: Avatars disappear/ grabbing doesn't work when the HMD is unmounted and then mounted

The detailed situation is as follows.

• When I put on the HMD and start the app, I don't have any problems at first; it plays fine until I remove the HMD.
• If you remove the HMD during the app , wait a moment, and then put it back on, the controller and hand functionality doesn't work properly.
• My app has some objects with grabbing facility, it doesn't grabs properly after remounting again (works properly the first time).