Facetime audio calls on iPad has no buttons

OS: 13.3.1

Device: iPad Air 2

Whenever my daughter receives a Facetime audio call, there are no buttons to accept/reject and she is presented with an opaque screen and cannot do anything on her iPad. If she calls out and gets a connection, then she is unable to hang up the call.

Even when opening the multi-tasker, there is a tile with the opaque look to it and it cannot be swiped up to clear it from memory...the only way to do so is to hard reboot the iPad.

I have searched Google and the Apple community but haven't found a way to resolve this. Has anyone encountered this before?

Note: Facetime video works without issues.