I've noticed when I charge my phone and my lock screen turns off, a blinking light appears briefly above the sensors next to the camera. I'm not sure if this has a function or is an issue. Never seen it before and doesn't happen when phone isn't charging.
This will probably be the Smart Stay function which checks if you are looking at the screen, then stays on if you are looking at it.
The light dot you see is the Proximity sensor, hope this makes sense
@TomaszT , never even have a thought to Face Unlock, that is a valid possibility