It could also be a motor drawing excessive current. I've seen motors draw 3-4 amps with no load and appear to run normally. If that were happening, I suspect we'd see about what we're seeing. The power supply on the DCDS motor driver is shutting down and then starting again, that looks like it might be seeing an excessive motor load. It's either an excessive load on it or the DCDS is failing in some fashion and shutting down. With shorted driver FETs, it'll also go nuts.
I REALLY doubt this is the magnet ring, it just doesn't fit the symptoms.
I stand corrected regarding the magnetic ring. The engine I had issues with did run, but very sporadic. It did not stop like this one.
I would agree with you that the issue has something to do with the DCDS.