Okay, so I spent some time examining the atomizer head on the Protank and found the problem. The rubber insulator can get pinched if the center pin is pushed in too far, thereby expanding the rubber. This then blocks off the airflow that would otherwise come in through the holes on the side of the 510 connector, down alongside the atomizer base, and then up through the middle of the center pin. Try pulling your pin and pushing the rubber insulator back into shape to open up the airflow. Also, because I've been rebuilding my Protank coils for a while, I've noticed that the rubber insulator is getting broken down and is not as stiff as it used to be, so that is likely why its getting smushed (for lack of a better word) more easily.