It isn't hard to pin down for me. I was with a new S100D, had a low state of charge, stayed with my car and tried all 4 cabinets. All of them peaked at a normal charge rate and then crashed within 5 minutes. There were no other cars at the supercharger.This problem is really hard to pin down. The car almost) always starts a high rate and then after people leave the car it drops. So most people don't notice it. They see the high peak rate at the beginning and think all is fine.
The charge rate drops down as the battery fills up under perfect conditions so again it is difficult to know what charge rate is normal at what battery level. It is different for every battery pack type and as we know also depends on the age and usage of the battery pack. And of course pairing of stalls confuses new owners. All this makes it very difficult to make a statement if a Supercharger is slow or if it's normal based on all the factors mentioned.
In the end, I got enough to make it to Grand Island and just moved on. Fortunately I only needed about 40-50% to be confident I could make it there.