For a while I had an issue with my vivi nova not sitting correctly on my iTasteMVP - I changed out the coil on it and made sure to tighten it down fairly well. When I had unscrewed the top, it backed out the coil on its
threads just a little bit, enough to make it misfire. I'd start there. If that doesn't work out for you, make sure you look at the
threads on both and see if there is blockage. It'd be a safe bet to just clean it with a q-tip with alcohol on it.