Ahhh...
Traction. Haven't seen the SR Traction, but I guess it's safe to ask, does the system use mechanical switches for all terminal slowdowns, or magnets? I ask only because some OEM's have had issues in the selector department due to small gaps between the magnet stack for NTS/ETS that the CPU sees as turning off/on at an inappropriate time and faults the car. Closing this gap corrects the problem. I've seen weak magnets on the 211, and the TAC20 cause intermittent trouble too in stepping or floor position.
You've no doubt already covered a good bit of ground on this issue.
Hope you get to the bottom of it sooner than later!