All messages in my inbox are marked "unread"

Have anyone else this problem?

Yeah. There's another thread here talking about it as well. 

Yes, same here. Marked "Unread" and "New".

I'm sorry for the confusion. the messages weren't really unread or users were new, it was a display issue. I worked on the messaging and inbox system to make it 1) faster and 2) compatible with the mobile app workings. this is now done and the display error is fixed on the web. P.s. you should see the inbox pages being much faster to load now, too.