Yes, we have the same problem. The recording lately are often unwatchable. I phoned faults and they say our box is fine. Last night when recording two programmes it rebooted itself in the middle of the recordings. Apparently as a loyal customer since the days of NTL we are not entitled to a free upgrade to the T6 box.
The resolution was that we should see if the problem resolved over the next few days. That was before the box restarted itself mid-recording two channels. Luckily BBC iPlayer etc will cover the missing recordings. It is too soon to be sure if the issue has fully resolved although to be fair the last couple of recodings have been OK.
Our box is the 1Tb Tivo with three tuners. We were told that we have to pay £99 to change for the current issue T6 box and couldn't keep the existing box (assuming it now functions OK) in another room without an additional subscription even though we only would want to keep it to access the recordings already made. As we already pay VM over £1,100 pa we are reluctant to spend any more especially since new customers get the newer tuner by default.