I had a Vaporesso Gemini RTA that was delivered to me DOA; that had a similar problem. The 510 positive screw just spun freely, and I couldn't get an electrical connection. When I turned the screw, you could see something (looked like a shiny metal bar) spinning around inside the air intake slots, that was obiously atted to the screw. If I put a toothpick through the slot, to stop the bar from spinning, the bar would thread up/down the 510 screw.
This deck has a modified velocity style deck (in that it has a tube running up the center of the deck that is supposed to provide additional air to the insides of the dual coils). As best I could figure, because the positive post was not directly centered over the 510 screw, they needed a means to connect the pin to the post.
This was the diagram I included in my e-mail, to the retailer that sold it to me, to help explain what I
thought was going on:
View attachment 718419
I also included a short video that demonstrated what the spinning bar looked like through the air slot. I never got any conformation/denial that my design presumptions were correct. But, they sent me a replacement deck, without any further questions.
I don't know how the bar was supposed to be attached to the positive post (if it was cast, press-fit, threaded, or something else). But, when I removed the 510 screw completely (thereby detaching the bar), I could find nothing else internally that the screw could reach/touch.