* I have next to no first hand experience with Zero motos or their drivetrain, reply is based on my EV experience *
Motors used in EV moto use position sensors to provide feedback to the controller about where the rotor is in reference to the energized coils of the stator.
This is used to calculate slip angle and adjust which coils are bring energized.
When this position is being reported incorrectly, stutters or inconsistent power delivery can be experienced at low speeds.
This issue can sound like damaged bearings.
If you are familiar with RC quads, planes or cars they use brushless motors that are sensorless, because these vehicles rarely see low rpm or high torque requirements it's not an issue.
Hardware issue would be my first guess but it's possibly a software one, seems there is some tuning (commissioning) that can be done.
On the physical side I would examine the plugs exiting your motor, it is possible one of the pins is not making good contact?
Also worth checking is your throttle assembly, I have seen one issue with the throttle unit used on the SR/F where the sensing magnet inside was broken in 2 pieces.