iMessages from 1 contact disappear after 18-24 hours

Only on my iPhone 16 Pro Max, since I bought it, imessages disappear after 18-24 hour. i can see them on my Mac and iPad and also my old 13 Mini, but not on iPhone. This is happening only to 1 contact (messages last up to 2016)

I already rebooted the phone after one week and things were working until update 18.1.1 when I notice the problem was there again.

I contacted multiple times Apple assistance and we went through all the normal solutions, but nothing worked. if I do search something inside imessages, past imessages from the contact come out: so they're there, they just don't show up on list.

I tried turning off and on imessages, removing and readding the contact, disabling and reenabling imessages... nothing at all.

So if there's someone out there who had the same issue and could solve it it will be great

thanks!

EDIT: I can also view and open and edit all the pictures, docs, and all the other stuff we exchanged in the last years. it's just the messages that aren't viewable.