I'm having the same issues with my BT Pro box. I've only had it 2 months and for the past few weeks when I try and watch my recorded programmes they just freeze with no sound. This can happen a few times during playback or constantly throughout the playback.
I've done a hard reboot numerous times by unplugging the box for 15 seconds and then plugging back in. Sometimes this resolves the issue but for a short period of time and sometimes it does help. I've rebooted the Internet hub numerous times too and this hasn't helped.
The only option left is to either do a hard reset and lose all my recordings which I'm not happy about, but I've heard this hasn't resolved the issue for others, or to have a new box and again I will lose all my recordings.
This is unacceptable as I've only had the box a couple of months and the money I am paying I would expect better service. Surely there must be something someone can do ?