Facebook Messenger automatically sets “seen messages”

My friend’s messenger on iPhone automatically sets “seen messages” even though she didn’t open it. It didn’t even show a delivered or sent status when I send a message to her. It just instantly shows “seen messages” of whoever messages her. Even right after I press the send button, it is already marked as seen. Why is this exactly happening?

We already tried reinstalling messenger and Facebook but it doesn’t fix the problem.

Is there a solution for this?