Make sure to click on “show all” button (or equivalent button of your app). Once visible, mark as read so they won’t remain as “active” message.

I had this behavior with my app that was considering the messages read (so hidding them by default when going to the messages tab) once i opened it while not marking it read on lemmy side (hence the 7 unread messages displayed)

Took me week to find how to solve that :-)