winter time duldrums. As you mentioned, it is more common during cloudy days, etc. They probably sense cold fronts and changes in weather during the winter much more than given credit for, even inside. My mali behaves the same way. To be honest, I have learned not to stress about it and just monitor the temps and her overall physical condition. She doesnt lose weight or exhibit signs of poor health when she does her day or so hide fests, and usually eats heavily and is much more active on bright sunny days (her cage is next to a window in the house).
I think in general, herpers overfeed or over offer food to their critters more than the animal needs. Then freak because they dont eat daily like a cat or dog would. In the wild, uros are probably eating whats available during certain times of the year, with whats available not always being the most nutritional, or anything at all being available. In captivity, they are probably eating much more nutritious foods consistently, and probably being overfeed from a nutritional and volume point of view. If you really want to feel stressed, try keeping ball pythons during the fall and winter months. My adults would go off feed from mid-october to late April. They would "turn on" when spring came around and feed like demons. However, they never lost appreciable weight or anything during the down time.
Sorry for the long response, but I think folks on this forum get way too worried about feeding responses. I think feeding variation is probably just natural to an extent based on time of year, etc.