Ugh,
I'm stuck in Flagstaff, AZ at an L2 charger because my 2015 S85D will not charge at the supercharger here. I'm seeing the exact thing others are seeing, '...Ring stays blue and says "starting to charge" and then switching to "charging stopped"." I was on the phone with Tesla support for about an hour trying to figure this out. I had not yet read this post. I'll paraphrase here, they said the AC/DC charging can get confused and stuck in AC mode and not allow the supercharger to work. They suggested I find an L2 charger (which was conveniently about 1 mile away) and let it charge for about 2 hours which should help "reset" the on-board charger. This is where I'm sitting while reading this thread and writing this post.
Having read everything in this thread now makes me realize the tech on the phone probably had no idea what he was doing. I'm not optimistic that after my 2 hours of charging I'll be able to go back to the supercharger and juice up quickly for the ride home.
Thank you all for sharing in such great detail. I think I'll be taking my car in for service when I get home. I'm still under warranty, so hopefully I won't be out of pocket anything.