Why do I get notifications for texts I then can't see?

[AC Question]

I have a Moto X with 5.1.1. I receive notifications for group texts that I can read while I'm viewing the notification, but otherwise have no access to them. There is then a number at the top of the text screen that appears to indicate unread texts, but I can't access them. However, if I access my texts with Moto Connect on my PC, I can read them. Any ideas?