Yes I've often blanked out when trying to listen to people, but not usually during small talk. If it's small talk, I can engage in it for a short time, and if it goes on longer than I have the engery for, I seem to go onto automatic pilot where I'm only partly there....as if half my brain is getting tense and giving the work to a different part of the brain. And I tend to forget most of what's been said afterwards, as if it was processed by part of my brain that doesn't bother to lay down strong memories.
It's usually "important" information that blanks me out - from a mediocre teacher or from anybody explaining anything I might be expected to understand and retain for some future purpose. It's usually fine if the speaker takes the trouble to be very clear what they mean, but any carelessness can throw me completely. I think it's the anxiety of thinking that I'll be in some kind of trouble for not taking it in, that shakes up my brain and stops me from focussing on it properly. Often I think that if only I had a transcript of what they said, I could study it in secure isolation and work out whether it was really too vague for anybody to fathom, or not. I'm sure that sometimes it's really their fault, but I can rarely know at the time whether a particular conversation is unclear because of me or because of them.
I get similar problems when trying to read certain books or listen to some spoken-word recordings, but with those it's easier to repeat the exercise and analyse the situation to find out who's messing up the dialogue, though there are many borderline cases, and I suppose these hard copies must be intelligible to some people, or they wouldn't exist.
Ironically, my schoolteachers were often very pedantic about the way we spoke to them.....when I told the deputy head that I'd forgotten my school tie, his reply was "so what?" - he wouldn't deal with me until I'd explained that I knew he had a few spares for just such an event, and would like him to lend me one, though it was obvious that he knew perfectly well what I meant. No doubt he was trying to educate me, but not for the real world in which most people just don't bother to be particularly clear. So now as an adult I have to tolerate loads of scruffy communications, though I myself didn't get that kind of co-operation from my mentors. It must be great to be an Aspie in a high position, and to be able to demand high standards of clarity. I'm sure I wouldn't blank out so much if I had that degree of control over the way others spoke to me.