Turns out the issue is faulty fittings at the top of the vessel (leaking air). Both BRS and the Distributor (Proline) acknowledged that there issues with a batch of 5 liter vessels (not sure if any 2.5's were involved). They did request the serial #'s to help them track the defective ones.
BRS offered to exchange them, but ground shipping to NY takes almost a week. BRS gave me Proline's # to see if they had a better/faster option. So I called Proline and they sent out 2 replacement tops today (the same day I spoke with them; 2-4 day shipping), and they said I could throw away the defective tops. Good customer service experience all around.