Grrr. I've snapped the axle inside my Bafang BPM rear hub. It's a brittle fracture of the hollow axle right where the cable comes out into the windings. 4 years old, but still, not good.
So now I've disappeared down the rabbit hole of trying to find a replacement motor-hub-wheel. The company I bought the bike from no longer sells that model, but maybe they've got a spare wheel. Otherwise it's going to involve trying to navigate the Hong Kong outlets like bmsbattery and greenbikekit.