The protank is seating too deep into the 510
threads, which in turn is blocking the airholes on the 510 connector.
Its not uncommon on V2's and V3's, unfortunately theres not really a perfect fix, its a matter of playing around till you find a balance, but you should be able to make it better.
Option 1: Using PT beauty ring to raise/support the PT, allowing the holes to sit high enough to get a proper draw.
Option 2: Get an airflow controller to go in between the V2 and the PT (this option has been reported to both work and be ineffective)
Did your Protank come with the conical beauty ring?