If it hasn't already been considered, sometimes temperature dysregulation can happen due to the inability of the hypothalamus to manage body temperature. There can be other symptoms as well. It took a number of years for this to be diagnosed in my nephew, although his problem is inability yo keep his temp down. Here is just one article on the topic: https://www.medicinenet.com/symptoms_of_a_malfunctioning_hypothalamus/article.htm

Has this issue ever been discussed?
Sue