Sounds to me like it's definitely your mod having trouble forming a connection with the tank. As others have said, check your mod's 510 connection to see if it has gotten depressed somehow, or stuck. Did it work at all, or was it like this from the moment you got it? If the former, sometimes screwing on tanks too tightly can cause damage to the pin, but if you have other setups working and it's been that way since the beginning it does sound like either a fault in the connection or an electrical issue.
If you try the above remedies and are still in the warranty period, I would probably warranty it. I lack the skill to do even the most rudimentary of electrical work, personally, but even if I were quite good at it, if my mod were under warranty I would replace it, simply because I don't much care for the idea of having to "repair" my mod myself if it's brand new. For one, I might void the warranty (that can happen) and also, I'd want to make sure I was starting out with a solid device.
Best of luck, the above is just my opinion as always. I hope you find a solution.
Anna