Yet just using "throttle" [no pedal assist] doesn't seem much better.
First and only theory: the torque sensor ripped apart after hundreds of miles of slip bang of the bad free wheel. I suspected this before trying the new motor or even before the old motor went out. (A lot of problems go away on their own, although not quite as high a % as health conditions.)
For confirmation remove the torque sensor and wire in a similar strain gage to see if the error message disappears.