Your trouble is always in the same hoist way location.
This might be a long shot, but have you checked the DBG? Might the car be leaning far enough away from the vane encoding optics that they’re not being seen at 9? Or causing the encoder roller to just skip a beat or three? The two optical readers should be set at max on the sensitivity adjustment screw. And can I asssume you’re running on a new floor table after the MSU replacement? It is unusual that the symptoms diminish beyond 9 either way.