freebeer
argh.  Twice lost my work.
short version:  mapbox/DG Premium zoomlevel 22 are new, I was not seeing them 3-4 weeks ago.
There's nothing there to cast a shadow; in my lost reply I posit a rolling gate like you mentioned mapped to the east, in an open position, obscured in tree shadow.
The long z20 Bing shadow is the tall thin tree, which also casts a shadow in ESRI - 2017-new-Bing.  I think there I see a shadow from the opened gate I posit.
The black area immediately around the white line I interpret as an optical artefact, seen around other high-contrast lines.
I suspect the two carparks are not completely physically separated.
Still just guessing...