That sounds like something’s binding at the rear. If it rolls forward but locks when you pull it backwards
and assist won’t drive the wheel, it’s usually either (a) the rear brake/rotor catching, or (b) a mechanical issue inside a geared hub (clutch/pawls or planetary gears).
Quick checks you can try:
- Lift the wheel and spin it; then loosen the rear caliper bolts slightly and re-center it. If the lockup disappears, it was brake rub.
- Unplug the motor connector near the axle and try rolling it backward again. If it’s still locked, it’s mechanical (inside the hub).
- Watch the chain while you roll the bike backward. If the chain wants to move, the freewheel/cassette body may be seizing.
If it’s the hub internals (common when it locks in reverse and won’t drive under assist), a shop can confirm and often replace the clutch/planetary gear set—or the whole wheel/motor if parts aren’t available.
Good luck—hope it’s just a quick caliper tweak and you’re rolling again!