If it's losing time gradually, like it did this morning, then it could well be time of the year.  It's slippery and often takes a bit longer to accelerate this time of year, and also drivers are instructed to reduce speeds approaching red signals to 10mph, 200 metres away, rather than the usual 20mph. 

That all accumulates over the course of a whole trip, and I note that it only has 1 minute of recovery time on that near hour long section of the journey.

I will go with "leaf slip season" ...

It is due to arrive at Chippenham at 07:30 - so you are supposed to have 4 minutes and it's a classic case that illustrates where just a delay that is ordinarily trivial becomes something serious.

Interestingly, when there were engineering works between Swindon and Gloucester, the Paddington to Weston-super-mare train made an extra call at Didcot, and as a result left Chippenham 2 minutes later at 07:36, becoming an official connection for those weeks.   That could not be a permanent change because there's a Paddington to Cheltenham Spa right behind it at Didcot, but there's no problem further west (not at Bathampton now onward) and it has a 12 minute wait at Temple Meads before going on to Weston.

I asked GWR^▸ (Great Western Railway) if the express could be timed to sit a minute or two less at Bristol, and a minute or 2 in platform 4 at Swindon and - well - they looked at me as if I had grown horns.  Apparently that would slow down the London to Bristol timing and be a very major degradation of service indeed, and cannot be done on a permanent basis.  Pity, because it would save Melksham to Bath (and Bristol) passengers 35 minutes on their official commute.   Perhaps that's the real reason for not doing it - the Delay/Repay claims?

Until moving to Melksham in 2016 I used to commute to Bath from Reading (Earley actually) 3 days a week, catching what was the 0726. And that was great; hardly anyone on it, until a load boarded at Chippenham. I suspect the pre-7 (the 0656 in my day) would be even quieter.

Only problem was I had to buy advance tickets a couple of months beforehand to bring the cost down from over £100 to something under £30 IIRC^▸ (if I recall/remember/read correctly). No digital option in those days so always had a pile of tickets waiting to used

And it's that Paddington express which prevents it running earlier to increase the margin THAT way ... quite apart from it being threaded through Westbury!

edit to add Westbury comment

Reading Real Time Trains, the 4 minutes (so unofficial) connection missed again yesterday by between 30 and 45 seconds. The delay to the 06:35 from Salisbury was picked up in the short stretch from Westbury to Trowbridge - on a 7 minute schedule from arriving Westbury to leaving Trowbridge yesterday took 12.  It was back on time when it departed Swindon, but of course that's too late in its journey for the Chippenham connection.

The train that left Chippenham spot on time as the train from Melksham pulled in arrived a minute early into Bristol at 08:02.    The next train to Bristol from Chippenham arrived there at 08:39 - 3 minutes late.

Edit to correct - the words had not come out right this morning and the original was unclear and incomplete - my apologies to members who were trying to work out what I meant!

Oh dear ... please keep logging.  The Coffee Shop will not get any "official action" on this frustrating issue, but it does keep it bubbling along and we are read.   No promises of a result, but a promise to try further for a practical change.

No idea when Chippenham's other platforms were taken out of use, perhaps the 5 minutes dates from past times.

Mark