I have been with the same problems for about a week. Never before.
Clicking on "Show unread posts since last visit" brings to a list of 2 to 4 unread pages. If then I click on "All unread messages", thy grow to 5 or 7 unread pages.
This is in various diferent devices.
I have Tapatalk on my phone but I don't use it. Maybe it checks the forum?