I’m afraid this is one of those random behaviors.
When I leave the work campus, the striped road dead ends into a local striped two lane road with a blinking red light. If the route involves a right turn, FSD-b does a creditable right-on-red and proceeds, just as if it was a stop sign.
On left, for months now, a left turn would have the car creeping up, shaking the steering wheel a few times, and then freezing. If one gassed it through, it would drive, sort of, but would keep on trying to freeze until about 50’ past the intersection, at which point it would come to its senses and take off.
Last week on a Thursday, it started to pull that stunt again then, to my surprise, after the halt, executed a clean left turn and kept going.
Map update? Self learning? Random number generator? Phase of the moon? No idea, but there it is.