I don't think its that unexpected that you might have some social difficulties in the beginning. During elementary school when genders were not as separated as they are afterwards, I was outgoing and could talk to anyone. By the time I transitioned, I'd spent the majority of my life trying to be invisible. Jokes about my masculine body language and dress made me turn inward and I started to feel as if everyone was laughing at me. It took a couple of years after I transitioned to stop thinking the laughter was about me when I would pass a group of people and hear them start laughing.
If you went through something similar during your pre-transition years, your social skills are probably a bit low and when people don't turn to you to converse, it may be interpreted by you as something you did or did not do.
When you join an established group of any kind, even support groups, it takes a little time to be accepted as part of the group. There may be some others who are uncomfortable being there themselves and shy. Keep trying to make contact with others in the group. For all you know, starting a conversation with someone who seems to be ignoring you might be a relief to them. They might be nervous and glad that someone is approaching them.
You kind of have to regain your self esteem, which is part of the transition process for many. Transitioning is not just about the physical changes you go through. Its also about finding yourself again. Realizing that you don't have to be on the outside anymore. I'll give you that it can be uncomfortable in a situation as you described, but consider it part of your personal growth.
sam1234