My granddaughter is now in the fourth grade. This is the first year she's wanted me to volunteer in her classroom because she's proud of me. Yes, she wanted me to be there before but it was because she wanted me for herself. She was unaware of what other kids thought. She was jealous if I paid attention to the other kids.
Not paying attention to you could be his way of protecting himself from jealous feelings. He may have "disconnected" with you without being aware that is what he is doing.
Or he may be ahead of "most" kids in his need to be independent and that could be a good thing. I suggest he could be trying out being independent and that once he's aware that he can still be independent while doing those warm things with you he'll go back to being "close."
So....not running up to you, hugging you, etc. doesn't mean that he doesn't still feel close to you. In fact it may mean just the opposite; that he knows he's close so he can risk not doing the touching sort of things. He can ignore you because he knows that you love him. He can try out independence.
His behavior doesn't necessarily mean he's embarrassed. Have you asked him why he seems to have changed? Have you asked him if he wants you to not come into the classroom? Have you been able to be calm and not let your pain show thru your questions.
One way to help get back to the touching sort of things you miss is to relax and let him take the lead. Say, hello to him in the classroom, be available for a hug if he wants it but don't push one on him.
Sometimes we overwhelm our kids with our own need for reassurance. Work on regaining your own sense of security before talking with him. Let him know that you miss the hugs but it's OK that he doesn't pay attention to you.
It's normal for kids to appear stand offish at school. I can tell you from experience that he'll figure it out and soon be back to giving you a hug if you let him do it in his own way.
As I was just reading other mothers' messages I remembered that when I went to my grandson's Grandparents and Special Friends program a couple of weeks ago he ignored me. He's 6 and in the first grade, special ed. Other times he's run to me and given me a hug. On this day an aide was reading to he and a friend. I knew my grandson had seen me but perhaps the aide didn't know that. The aide stopped reading and told my grandson I was there. My grandson looked up and looked confused before he quietly ran up to me. Quiet is unusual for him.
I think that he was in his own world, a world in which I didn't play a part for him. His lack of enthusiasm and a hug had nothing to do with me or his feelings for me.