Lehner 3080 / 8 Brushless Motor ? fault

[What's_nitro?]

It's the controller that's the problem. Motors are (for the most part) passive devices. Something like this where the motor stops at low speed and wont start sounds like, as others have suggested, a commutation problem, or, start power is too low. I would bank on the latter since you can stop it by hand at low speed. It could be a radio issue, IDK maybe the endpoints the controller was programmed to became corrupted so it's missing a few steps on the low end (in the ESC, not your Tx). I'm assuming the motor has no binding at all at any point, and there are no shorts in it's windings.