The Vivi is a tighter draw than the Phoenix. No doubt about that. But after reading your post, I pulled out my long neglected 510 battery and screwed a Vivi to it. Sure enough, it was un-vapable with only enough threads engaged to where it didn't fall off. On my 510, the connector is not letting enough air in and an extender will fix it. The side holes are only supplemental. Most of the air is coming in from the center post and some connectors block it.
That said, there should be 2 notches on either side of the air hole in the center of the connector of the Vivi, I have heard of a Vivi that didn't have those notches. So that's a possibility. Otherwise, it's your battery connector.
[EDIT] I just tried it with my 510 batteries. This time, the draw was o.k. So, I take that back. But check for those notches. If it's not your batery, then there's no other logical explanation.