BLUE TONGUE SKINKS

I have 4 year old Halmahera who for the 4th winter seems to be going into brumation. I have researched and found that they have the ability to do so but only will if the temperature is low enough? The temperature in his setup is the same all year long so im not sure why he is doing this. In the summer and shoulder seasons he acts perfectly normal but, around November he always stops eating and only comes out to bask every few days and moves between his cool and warm hides occasionally. Im also sure he is a Halmahera and not an Australian species which if he was, would make more sense. The humidity is also appropriate for Halms as well. I’m just trying to cover everything that might be causing him to act like this.