After a recent software update I notice on my Samsung Galaxy S7 Edge, a cast icon in the top left hand corner of my screen. If I expand the notification bar it looks and says the following: Cast device not connected.
I cannot flick it off the screen, however if I long press anywhere on the notification the App notifications page for Facebook loads. By switching off the “Allow notifications” and then turning it back on, the Cast notification disappears.
I am not sure if this has anything to do with it, but it removes the cast icon from my notifications.