FaceTime Button?

Anyone that’s been running iOS 11 B1 or B2 have you noticed during FaceTime call a greyed out button off to the bottom left corner?

It appears in beta 1 there was not an option to alternate cameras to the rear camera during video FaceTime calls-that seems to have been fixed now in beta 2(the option to rotate the camera is in the small view of yourself during video chat)however there is still a greyed out circular button in the bottom left hand corner during video FaceTime calls.

Does anyone know what this is I missed it or it’s an unknown thing maybe?

Thanks