I never really attributed that to autism... but social awkwardness in general-probably because I've seen it happen a lot, and it's happened to me... meaning, either the other people have stopped talking to me, or have told me of a story of why they stopped talking to so and so, seen others question why someone quit talking to them, or because I've stopped talking to someone. Not everyone I've encountered has autism, so it can't solely be due to that unless the conversation halts as soon as I mention that I have it... in that case, it's a possibility.
I've done it to others, not because I'm trying to give the cold shoulder, but simply because I just don't know what else to say. If a response was expected, I usually figure somebody would just message me and say, "hey, did you get that last message?" Then I would know they wanted me to respond.
But if the message was just stating facts or something we previously discussed already, I have a lot of difficulty responding.
Or if someone says something like "anyway, I just wanted to say thanks", then I just figure they literally just wanted to say thanks, so I say "okay" "You're welcome" and move on.
It's rough... I do it a lot in real life too... just stop talking. I'm not trying to be rude, I just don't know what to say, or figure they are just stating facts. It's really bad if it shifts to something I just can't relate to at all, because then I'm at a total loss. Sometimes I'll just say "I'm lost", but then sometimes things are so over my head I don't want to invite more confusion with someone trying to explain something to me that I likely am not going to get... and sometimes I say nothing because I don't really want to admit just how incredibly clueless I am.
I have a hard time balancing that online though... sometimes I forget that I actually AM communicating with other people and I treat it as such at times.
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Sorry about the incredibly long post...
"I enjoyed the meetings, too. It was like having friends." -Luna Lovegood