Some channels (usually the main ones) are better than others with accurate record and their adherence to EPG times.
Humax’s reference to 2 satellites is related to the fact that the freesat transponder is at a slightly differing position. Signals from the freesat transponder should be similar to say CBS Action which is on the same satellite.
Happens to me also on the occasional recording from one of the less well known channels (CBS, True Movies etc). Almost certainly down to the broadcaster not setting the correct start/end tags. Humax talking rubbish.