Ask HN: iPhone Camera on indicator

No Apps open. Face ID is off. Why does my green 'Camera on' indicator on the iPhone come on? It particularly happens when unlocking the phone. Could it be camera is turned on before the phone detects that FaceID is off? Or something more nefarious? I would really like to know if an image is being captured or analysed and by what app/process. Note again, face Id is off and no apps open.