Clean the optos, and make sure the set screw that attaches the spider is securely attached. The spider should not spin freely without engaging the motor. This is probably your issue.

Did you run the Spider Test option in test mode? You should do this when the machine is "fresh", and at the point of having issues. This way you can see if the behavior is different.

This should point you to the correct fix, and be more clear if the motor has an issue.

First place I would check is the set screw on the spider pointer like T7 said. I have had the same issue with mine and that is what the problem turned out to be. I even put a little lock tight on it to prevent it from happening again. It is a 1/16 hex key screw , I think I had to remove the board from the back of the spider motor to get at it easier.... Good luck

Be very careful not to over tighten that set screw. You can crack the plastic if you go too tight. Then you're really screwed ... pun intended.

Just make sure it's nice and snug.