You message suggests that the washers are bolted at the holes on the
circumference of the ring gear. IIRC, your prop model has the extended
hub. Extended hubs do not respond very well to balance correction at the
ring gear because the plane of correction is not close to the plane of
imbalnce. Sure, a balance can be achieved but the amount of correction
weight will be 30-50% more that if placed closer to the plane of imbalance.

After the prop is installed again, the final dynamic balance should be
checked above 2300 rpm. 2000 rpm readings are not valid.

Kent Felkins