If it's only doing this on recordings it sounds like a faulty hard drive, try pausing a live TV programme for a minute or two and then restart, this uses the hard drive, if this freezes and skips then it is looking like a call to Virgin for a replacement box.
Thanks for confirming the requested details via PM
I have booked in the next available engineer visit on the system for you so that the box can be looked at and replaced if needed. You can manage your appointment time slot via your My Virgin Media app or account here: virg.in/myVM
Let us know how the visit goes and if you need help with anything else!