As others note, Left Auto Lane Change worked fine and then it didn't-- and hasn't. I asked for service for this problem, which was scheduled for today. Last Friday I received the following from Tesla Mobile Service:
Hello, This is Robert with the Tesla Mid-South Service diagnostic team. I've identified the problem with your vehicle. The issue is due to a firmware bug that is not allowing the vehicle to do Left side lane changes. The Autopilot team is currently working on sorting this out and a fix should be available soon, and will be sent OTA to your vehicle. Thank you for your patience while we are sorting this out. I'm going to cancel your service appointment as there is no actionable repair at this time.
In the meantime, I find Auto Pilot (and therefore my Tesla) fairly useless. Every time I need to change to the left lane, I have to pull the car out of AP, make the lane change, and engage AP again, and again, and again . . .
Assuming we all have the same faulty firmware, I'm rather surprised this is not a MUCH bigger issue on Tesla forums.