Messages missing after transfer - CONTACT messages on one phone, NON-CONTACTS on the other

iPhone 15 Pro and 17 Pro Max

I have all my messages saved dating back to October 2014.

Created backup of 15 Pro on computer, installed on 17 Pro Max. All seemed fine.

It has now come to my attention that for all messages from 2014 until a certain date (2020ish), only the messages from NON-CONTACTS are on the 17PM.

Meanwhile, on the 15Pro that had all the messages a week ago, the CONTACT messages remain, but all the old non-contact messages have been deleted. I have not deleted anything off that phone.

I checked a contact card on the 17PM who sent me one message in Oct 2014, and when I click the message icon, it opens “Create New Message” and I can see the message from 2014. Their message thread now shows up in messages, but disappears after I force close the app and reopen. So the data seems to be there just now showing.

I also have an old 13 in my possession that I don’t use, and I do use iCloud to back up messages.

Any idea why this is happening or how to fix it? I don’t mind the missing messages on the 15, I just want everything showing up on the 17.