It's only a possibility that it's anything to do with the sensor, but checking that area will also give you the opportunity to check the tightness of the final drive screws. One of mine was loose.Thanks, I'll check this soon, sounds the most likely, except the bafang is not any clever torque sensor, just a cadence sensor I understand, so if cracked or broken why logically does it only affect high amps, not high cadence.
This isn't a picture of mine, but I swiped it from the net to show you what I'm on about.