The brain has a natural ability to repress unpleasant/negative memories to protect one's psyche. This is probably what is happening. His brain knows he feels shame/fear/anxiety when he goes there.
My H is doing the same thing. I'm a very linear person - I think in terms of dates and places and times. He really dislikes questions like, "On X date, when you did not respond to my texts or calls, what were you thinking?" I know now, that because SAWH was starting his A that he was in fantasy land pretending he was not a 39 yo man with two kids and a wife living in the suburbs. Doesn't make it right, but it explains it. Also, MC made a point of saying that there are going to be things that don't have an answer. Try not to get hung up on those things. She also reminded H that this has been a trauma for me and asking 1000 times is going to be part of the process to get over the trauma.