i was having the same problem. the axle adjuster cams have quite a bit of play in them. the secret is to get the belt set and torque the cone nut while making sure that axle nut on the other side does not turn at all. its easy with two people. the amount of play will make it appear that the cam has not moved ( i marked mine ) but if the axle nut moves then it will loosen up-good luck 
I have tightened the axle nut with the tire both on and off the table. Definately holding the solid axle nut while tightening the cone nut. I believe that the chrome is causing the axle to move on its axis. Have checked the torque on the axle and it has not changed.
I did not grind the chrome completely off the swingarm and adjuster cam, but I did make the surface rough. If this does not work then I will grind off the the chrome from the adjuster nut completely and try again.
If that does not work, then I will try another axle with no chrome.......then back to the stock swing arm.