When a snake goes off it's food, there are a few possible reasons why.
The first reason being it's enclosure. Have you made any changes to it lately such as taken away a particular hiding spot it liked? Have you moved the enclosure into a area in the house that gets more traffic moving past it that may cause the snake stress?
The second reason is housemates, although you only have one spotted python, housing snakes together can cause some problems. If the cage is not big enough to accomodate the snakes correctly, fights can break out between housemates over such things as hide spots, basking spots and more dominate snakes bullying younger, more timid snakes.
You also mentioned that you checked Montey for illnesses. Have you only checked for external parasites such as mites and ticks, or have you checked for internal parasites such as worms and canker. If possible, get a stool sample and have it checked out by a vet, they can tell you if the snake is carrying worms or not. As for canker, you can check for that. Canker will appear as a white-yellowish cheesy substance that appears around the snakes mouth region. Canker can cause things like not allowing the mouth to fully close and destroying teeth and gums. Canker isn't to be mixed up with a similar looking substance that is found in severe respiratory infections. If any illness is found, consult a vet immediately.
Another possible reason may be a change in routine. Have you done any thing different lately in terms of food offering. If not, perhaps you could try "braining", this is where a hole is poked in the head of prey to expose some brain and juices ( yes it sounds disguisting but is a popular method for troublesome feeders).
As you mentioned in your question, winter is arriving and your snake may be wanting to go into an earlier hibernation due to temperatures getting colder faster in you area.
If the snake is not losing any significant mass and it's health isn't deteriorating, i wouldn't worry, but if it makes you feel more comfortable, go see a vet who may be able to assist Montey.
I hope this has been of some help, my spotted python is a great eater and always has been. However, i own a spotted python with scientific name "Antersia maculosis". I think there is two pythons with the name spotted python which can get confusing. One is Australian and one is American. Hope all goes well