Whenever that happens just open and close your SteamVR overlay once and the hands will start working! :)
Alternatively you can hit "start" and that'll make your hands work right away, then you can go back to the main menu and do whatever.

If you want to prevent it entirely make sure the overlay is closed while the game is loading, it's an issue with the hands not starting up right if the overlay is open during a loading screen.

Thanks-
I had to reset my SteamVR to fix it-
also sorry for the poor grammar I was typing that with my headset partially on.