Green camera light

Hi, I have two iPhones, one personal, one for work. One phone has Snapchat and the covid tracer app that have given camera access, the other phone has zero apps that have camera access - after reading multiple threads on here I have triple checked this. I have noticed that the green dot appears at the top of the screen while the phones are locked quite a lot, especially when I take them off charge in the morning when I first wake up. I have checked the notification centre, and nothing is showing as to what could have used the camera on either phone. Why is this happening?