Just to say, I have just got the 5000T version and am experiencing the same problems. As a common problem, it may be Freeview Play. It is adhering to the programme guide time rather than signals sent from the broadcaster.
As a temporary measure, I have added 3 minutes padding but will get on to Humax.
Posts #1 and #2 are discussing two different topics.
#1 is about concerns a programme that started to record late and also
not according to the schedule, while post #2 concerns programmes where the announced schedule that
is being used for the start.
There are a few reasons that a programmes start time may not be ideal.
E.g.
(1) Not all broadcasters use these "signals" and some of those who do then do not use them on all their channels. E.g. UKTV appear to only use them on Really, but not Drama or Yesterday., while BBC do not use them on any radio programmes frequently resulting in truncated dramas, soaps (Archers) and documentaries
(2) Occasionally the broadcasters, or a party in the supply chain, that do use these "signals" mess-up.
(3) This year ITV and BBC have had a new playout mechanism. This has been blamed on a surge of programmes defaulting to scheduled times, or being inaccurate. At least one of those two broadcasters has admitted there was (still is?) an issue.
(4) For live events sometimes an additional process is involved for the "signal". This complicates any retrospective analysis and not all recorders may cater for that as well as some others.
(5) On the Humax freeview recorders interpreting the "signal" may not be 100% successful when the recorder is tuned into channels from more than 1 transmitter.
Have been very happy with my 4000T but recently scheduled recordings are starting 5 minutes late so I miss the first 5 minutes of a programme, and often losing the end too.
For example set start 18.30 set end 19.00 - but recording starts at 18.35
It may be due to being tuned to more than 1 transmitter.
It is difficule to guess with an degree of success as you've not given any specific examples of a programmes and channels or additional detail like what else you were watching or recording at the time. Also stating whether you are in range of multiple transmiters and what they are, and which one you 'pick' for tuning, may also help.