Sounds to me that either some grit is caught in the check valve or it's failed for some reason. The back part of the connector (behind the convenience wall) is a check valve to prevent that from happening. Since the rig is new, it's a warranty issue, but not hard or very expensive to fix on your own.
Dick, Joyce, Diego, Picatso and Gustav
2017 3720 RL, and 2013 HC 343RL
Pullrite Hitch, IS, Disk Brakes, 3rd AC, Winegard Traveler, Bathroom door mod, Dometic 320, couch for desk swap, replaced chairs, sun screens, added awnings, etc.