I think when they don't respond they may be in their head . Some they can come to a place were they respond to their name. This would probably vary from kid to kid.

Our daughter didn't respond or look at us much when we called her name. We did a simple test by asking her to touch her head or raise her hand or whatever. We would say, "(Name), if you can hear me, touch your nose." Teachers like our idea because then they could tell if she was listening even without eye contact.

I went through the samething with my son before his diagnosis. Which I really didn't believe at first, until I learned more about the spectrum. My son was high functioning but didn't talk, more like grunts and pointing. I thought he was ignoring me or something was wrong with his hearing, Not at all. His therapist encouraged us to come down to his level when engaging in conversations which also help with getting him to make eye contact. It didn't take long before he began to respond to his name. Also having play time with him helped to break his focus on things he seemed really in tune with. I hope this helps, even if it's just a little bit.

I find my son responds more to his nickname (boo boos) than his actual name and I think it has something to do with tone. We use his nickname in a more sweet, fun tone, and use his actual name in a more "knock it off" type of fashion a lot of times lol. So it makes me wonder if he associates his name more with us having a behavioral issue with him, I know he responds to it more when I change my tone to a more sweet fun manner. It astounds me how much they are in touch with our emotions then we give them credit for. Anyways I don't know if this answers your question but it's something that I've noticed.

Having an exam by an audiologist who works with kids with autism could help diagnose Auditory Processing disorder