imessage split in two

A few months ago I renamed my husbands contact as a nickname that I have for him. I went to the text thread and it was renamed to the nickname, I sent him a text and all seemed well. Suddenly I noticed that I have two different text threads with him. One in his nickname and one in his actual name. He only sees ONE thread and when he texts me, I never know what thread his message is going to come through in. In fact this morning I sent him a message in the nickname thread and when he responded, it came through his real name thread. So confusing. Is there ANYWAY to fix this? I am on a 14 Pro Max and he is on a 15 Pro max and we are both running iOS 17.5.1. Thanks for any help you can give.