iMessage goes to two different people

The weirdest thing has been happening with iMessage for the last maybe two years or so. My wife and I have two friends, let's call them Nancy and Linda.

When we have a group iMessage with me, my wife, and Nancy, iMessage also shows our message history with a different group with me, my wife, and Linda, but replacing Linda's name with Nancy's. The group message history shows messages that both Linda and Nancy sent us.

A few days ago, Nancy messaged by wife and I. We have a conversation over iMessage. All good.

Then, today, Linda messaged my wife and I. Her message showed up in the group chat from Nancy a few days ago. In really small text under Linda's message were also two notes "Linda added Linda to the conversation Today 12:24 PM" and "Linda removed Nancy from the conversation Today 12:24 PM". Then later my wife responded to Linda in the same thread. It replaced Linda with Nancy (on my phone and my wife's phone) in the "2 People" at the top of the conversation and in the headers above each message, and then in small text below my wife's latest message said that she added Nancy to the conversation and removed Linda from the conversation (which she did not). I checked with both Nancy and Linda, and they BOTH got the iMessage!

Linda and Nancy have met a couple times but hardly know each other. Like I said we've this exact problem, with these two exact people, on and off for a couple years now. We've changed phones since then even. My wife and I are both on iOS 13.5.1, but were on other versions of iOS when this started. No idea what started it. I double checked the contacts in both our phones and Nancy and Linda's contact records do not shared anything in common (they do not have any of the same phone number or email addresses) and are not linked to any other contact records in our phones.