Are the recordings manual or series links ? If they are series links are they on channels known for swapping programs from one channel to another (Sports channels) are guilty of this.Has it only started recently or has this been ongoing for some time. Try 1 manual recording and see what the outcome is pick something short like a 30 minute broadcast. If you still have the same issue you might need to call VM and choose Tv faults.
Are you saying that programs are running late, and your recording isn't covering the *actual* broadcast time? If that's the case, you can add padding to your recordings to start early and/or finish late.
Are you saying that you have, say, an hours recording which stops playing at, say, 45 minutes? The obvious question then, is whether all recordings are affected or perhaps certain channels.