Over the years I have read a lot of criticism of Mulder's behaviour on his return - in general and towards Scully in particular. The criticism is that he is being cold and uncaring. I believe he is being depicted as having PTSD, especially as he refers to trouble, 'processing,' things, which is a particular term applied to PTSD. I know quite a bit about this, as I have PTSD myself, although not from alien 👽 abduction and torture!