AirPlay works with Mac, NOT Class iPads

I have an Apple TV in my classroom along with a cart full of iPads. Just very recently, none of the iPads will AirPlay to the APPLE TV anymore despite being able to do so for over a year. All of the devices are updated (the iPads and the Apple TV). They are all on the same network. To make it even more odd, the classroom's iMac WORKS with the Apple TV/airplay!!!

The AirPlay icon pops up for the iPad... But after I turn it on and turn on mirroring, the AirPlay "menu" disappears temporarily.

Is this due to a recent patch or update?

Help please! Thanks!!