Are you testing this without any brass as should be. Depending on when the shell plate as made it may or may not have a slot cut for the EZeject nub on the base. In this case the shell plate will not go all the way down when securing it. The only time I see a shell plate not advance is when the primer seater is not fully retracted, primer sticking out in brass, and/or paws adjusted too high.
Does the shell plate turn easily by hand? If so I would look at the paw adjustments. Watch it closely while you operate the ram slowly. If it's binding on the paws you should see it.
If you have brass feeder installed remove the pusher foot till the ram operate smoothly. The same if using a lockout die.