It hasn't happened with my Alphas, but has with other planes. One thing that sometimes works is to make a washer out of sandpaper the diameter of the prop hub. Put it between the back of the spinner and the thrust washer of the engine. Not sure what you are using to tighten the nut with, but you should use a good size crescent wrench or box-end wrench. The 4 way glow plug wrench won't apply enough leverage.

Good luck!