A couple of things to try ...
- Unscrew the deck from the base. Make sure the positive screw pin in the deck (holding the positive deck down) is screwed in tight.
- Push the 510 pin out of the base, make sure it's clean, then re-insert.
- Screw the deck back on to the base, as tight as you can get it by hand.
- Before screwing the Lemo 2 on to your atomizer, take it and push it hard against a solid surface. While pushing down, move it around a bit too. This should hopefully set the pin snuggly in to the rubber insulator that is holding it, and also assist with making a solid connection to the positive screw.
If none of that works, you may need to (gently) push the insulator that holds the 510 pin up in to the base a bit further.
My three Lemo 2s were all OK from the factory, but I have started to have some connectivity issues that appear to be increasing my resistance. Every rebuild (1-2 times per week), I do all of the steps above after a thorough cleaning and they've been holding up very well.