Ours is a V6 box and our problem is identical to that described at the beginning of this thread by Peter-M (other than ours is apparently a v6 box powered by TiVo) :-
Our Tivo TV is intermittently crashing after rewind or fast forward.
After a fast rewind, the sound stops first, then the screen goes black, then comes back after 20 seconds or so and its ok again.
The Tivo box start up screen does not show (so the Tivo box has not fully rebooted) and the LG TV screen does not show (so the TV has not fully rebooted).
It happens when watching live or recorded programmes.
Been fine for years but started this a few weeks ago. It is intermittent but happens several times per day.
The last significant entry on the thread was that an engineer would be visiting so I wondered what the result was.