When you say you have 3mm play between the propeller and the shaft, i am not sure where the play is. If it is fore and aft and the cone is fully tightened, this suggests that the spacer behind the propeller has been left out, or something is wrong with the way the rope cutter was fitted. If the play is on the diameter of the shaft or more likely in the direction of propeller rotation this suggests wear on the splines within the propeller or on the shaft. This may have been caused by the propeller not being fully tightened and severe loads caused by the rope cutter doing its job.

We have a rope stripper fitted on Saloma and i am aware that it would be possible to tighten the propeller without engaging the two drive bolts from the aft side of the rope stripper into the holes which need to be drilled into the front face of the propeller. This would cause a problem similar to that which you appear to describe. The holes and drive bolts have to be aligned by rotating the rope stripper as the propeller is slide onto the splined shaft.

I would be interested to know more about your problem and how you get on.