MS Teams Share Button Disappears on iPad App

Hello,

We are running a virtual school in our board.  Our teachers are using iPads to share their screens with their students.  Everything had been running pretty smooth with that for a couple days, and then last Friday the Share button would appear and later disappear.  We weren't able to get this share button back.  We did quit the app and load it again.  Sometimes this worked, and other times it didn't.  Why is this occuring?