Long story short, I was told by Tesla this AM that there is a known technical issue with one of the chargers at the Dedham, MA Supercharger. I was using Stall #2B, charging started normally, but after a few minutes there was a sharp drop in the charging rate when my battery was barely charged. So I called the telephone number on the charger (same number as roadside assistance) and was told that charger had a known problem. It was suggested that I move over to stall 3A, which I did once it was available. A technician is due to inspect the equipment (no timeline given).
I had had reduced charge rate at Dedham 3 or 4 times in the past month or so and was beginning to wonder if it was my car. But I was assured it was nothing about my car.
Unfortunately I did not ask if the technical problem is restricted to stall 2B or if it affects other stalls. Someone pulled in next to me, using stall 2A, and said his charge rate was fine. So it may also be sporadic or it may be limited to that particular stall.
So if you charge at Dedham, be aware of the possibility that stall 2B, at least, may have a limited charge rate.