In the iPad app the inbox shows unread notifications as a badge. When you tap on the icon a list pops up with the unread notices subtly highlighted in light blue. After you tap on one of the notices the icon badge and blue highlight disappear... Until today. Now the highlight does not reset, and the inbox icon badge reappears with the same number a few minutes later. It's worth noting that all the notifications I'm seeing are old ones from a few days ago that I had already read.
On the web interface the badge is absent but the 'unread' highlight is visible.
After visiting the inbox on the web, the iPad is back to "normal" for now. The badge and blue highlighting is gone.