Messages disappearing on messenger

Hello,

I’m hoping someone can help me. A couple of days ago a friend started a new message thread on FB messenger. For him, he sees the entire conversation from the very first message. For me, I can only see like 25 messages, and whenever either of us send a message, the message at the top of my thread disappears. We live in New Zealand and are not using vanishing mode (it is unavailable to us in NZ so this isn’t it).

I’ve never had this problem before and none of my other chats have ever behaved in this way. I’m really confused as to what is going on.

Does someone know what settings I need to change so the messages we send each other remain in the thread?

Thanks in advance