messages not displaying from one sender

I can get to the users messages by looking up in contacts and then selecting messages. I get a notification when the user sends me a message.

However, the new message does not appear at the top of the stack.

The user has sent me numerous videos (tik tok, etc.) and i am wondering if it has become so large that it cannot be put on the stack.

otherwise have no idea what is going on. they are also an iphone user.