I am one of these people, I have no proof but believe it to be caused by too high a temp and lack of UV light.
This how urban myths start - you have no proof but you "believe..." What does that actually mean, and how is it helpful to the OP? Your theory is simply a theory without any evidence whatsoever,
and not something that needs to influence the OP. Diamonds can indeed encounter very high temperatures through the warmer months, throughout their range. They will bask (usually mornings and late afternoons), reach an optimum temperature and then retire until the heat of the day has gone. Like all pythons, they DO NOT need UV, it won't cause them any harm, but it is not necessary for good health.
From what the OP has said, I would be concerned that it either has not fed, or not been offered food, for more than four months during the time of the year when it should be feeding ravenously. In most cases Carpets & Diamonds which are well adapted to captivity, as this one should be, will feed as soon as food is offered, even on the first day in its new home. It looks like there are husbandry issues - too cool, and not enough heat for long enough during the heat cycle. A basking spot of around 34, with sufficient space in the enclosure for the animal to remove itself from heat when it has reached that optimum temperature. If the perforated metal sheet in the picture runs right across the bottom of the enclosure, it will keep the lower levels of the enclosure from getting suitably warm - convection will draw large amounts of cold air into the enclosure right across the bottom. In my experience, whenever Carpets are reluctant to feed, the first thing to look at is temperature. This is clearly a well acclimatised old-timer, and should need little or no time to "settle in." Unless there is some underlying health issue, the problem will be related to temperature. Four months without food during the period of peak activity, while it won't damage the animal in the long-term, shouldn't have gone unremarked for as long as it has.
Jamie