@jwz I had a ridiculous bug in iMessage where every time I messaged my friend, it would create a new 20 person group text with random contacts. So when my friend replied, it went out to the group text.
Every time I removed everyone from the group text and started over, we’d get a new group chat with 20 new random people in it.
Nobody could help me. When I updated to a new iPhone, the entire chat history from my friend was completely deleted. But hey now I can message him again.