2 Unread Messages for weeks and months without seeing listing anything - eviltoast

My Unread Messages is at 2 (it was at 1 for a month or so, but since weeks its at 2 now). Clicking it shows nothing. Maybe there are messages from people I blocked? When I get real new unread messages, then counter goes up and it works like always. Reading those messages (or clicking them as read) will decrease the number, up to 2.