Bafang BBS02 motor cut/restart

Hi All,
I have a problem with a BBS02 mid drive, 350W 36V. The motor suddenly cuts out, then back in within say 1/4 of a second. It's like the power to only the motor was turned off then back on, power returning with an audible clunk through the internal gears. It's not like the power interruption from brake switches or gear sensor where the motor smoothly stops and restarts - this is sudden.

It happens with brake & gear sensors connected or not, and with the BBS unit swapped to a different bike and battery. It does it under load and no-load.

When it does cut, it is always with the cranks at a particular angle, but it doesn't do it every crank rotation...

The BBS unit has been back to the retailer who could not fault it but still changed some internal components as an attempt to fix it. (incidentally, based on a video of the problem they agree it has an issue, but can't replicate it.) The retailer's sending me a new unit, but I'd really rather like to know what might have been the problem.

Any thoughts at all?

if it happens at a particular angle, then it is almost certainly the internal pedal sensor(s).

what exactly it is doing to cause only intermittent cutouts at that angle, i don't know. but most likely it's a misalignment of the rotating magnets with the sensor itself, perhaps a broken mount on either the magnet ring or the sensor, cuasing it to have just enough play to move far enough away for long enough that the unit no longer detects crank rotation and shuts off. that type of problem may be difficult to see.

if there is more than one sensor in the unit, it oculd also be that one of them is intermittently failing (wire disconnect, or even wire shorting signal to ground or signal to 5v, etc) causing essentially the same thing. but i think there's only one sensor in it.

Thanks Amberwolf,
That's a good lead and helpful.