The only observation I can add that might give someone else a clue, I recently saw the same “Maybe..” plus persons name following updating there phone number. I had a number of texts in one conversation from said person, with there phone number in my Contacts, they then changed Sim (with different tele number).
I first added that new to the Contact, message still displayed ok with there name, but when they told me the old number was no longer active I removed it from Contacts, that’s when there name altered to “Maybe“ plus name on the text conversation.
Couldn't get rid of the “Maybe..”, even by getting them to send me a text, on the iMac text was added to previous conversation but had the new number showing, and on iDevices the text started as new conversation - this done my head in so decided to start from scratch by deleting all texts on all equipment.
ps. if no number has been changed you could try sending or receiving a new text for that person to see if it kick starts something!