Camera didnt record

My floodlight came on when someone trespassed tonight. I did not get an alert - I just happened to be by the front door when i saw the light. I ended up calling the police but have no video , just a still as if someone appeared then disappeared. I do have the Protect Plan. In my video feed, i have a still shot of the man in my driveway. The Ring did not record anything as it was supposed to. What settings are wrong on my camera that someone can be in the frame that long and not trigger the device? I have a fairly long driveway. I know that cars driving down the street trigger it, but not a person?