I'm guessing you have 2 separate recordings, the first part & second part separated by a gap of perhaps 5 minutes.
As mentioned above, this usually means your box has rebooted, and resumed the recording for the second half.
A box that's regularly rebooting has a fault, and depending what the programme was that was affected - you may be able to find alternative showings and record it again. Your other option, from either of the recordings, just below the "play now" option will be a "related videos" link. If the programme is available anywhere on VoD, it should show here.
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