I doubt there was a direct visibility. There was a slight turn in the street.
Today, the connection has disappeared 2 times. And always around 350-500 meters. I was embarrassed only by the fact that the manufacturer stated that Maviс 2 pro should keep the signal more stable in the city, but it lost it in the small town (village) after 300m fly.
Sadly, it is very true that Mavic 2 EU version (don't know about FCC) can't go above 400 meter and this may have been future in RC to decrease the signal intensity. I have experience that same issue like you had. I was just testing my new Mavic 2 Pro Zoom (CE) in UK and I was flying from the centre of 100 meter wide open ground and I could lost the signal around 390-420 mtr and I also try orienting antenna directions as well as RC but neither helped.