As linked to in the FAQ for IGT Error (Tilt) Codes and Resolutions (
here), 3300 is a Hopper Empty error. The machine is trying to pay out however many credits were on the meter when someone hit the "Cash Out" or "Cash/Credit" button (depending on the legend insert), and has decided that there aren't any more coins in the hopper since it hasn't seen a coin exit the machine in "x" number of seconds.
You mentioned that the machine does pay out one or sometimes no coins after you close the door. Although 10 coins in the hopper is a pretty low amount, it should be able to pay out most of them. Chances are that the hopper knife is either broken or misaligned, causing the coins in the hopper to not be diverted to the hopper exit. As the hopper spins and no coins exit, the machine then assumes that the hopper is empty and throws that error code.
Search in this section for posts about the hopper knife to learn its function in the hopper and how you can try to adjust it to get it to pick up the coins in the hopper from the shelf wheel.
As Harvs said, the machine just needs to finish its current cash-out right now. You cannot stop that by pressing the self test button or turning the jackpot reset key.