Give Lippert a call they are very good to work with. It's most likely a check valve stuck somewhere in the system. We had it for about half a year and scheduled to have it fixed at the national rally. By the time we got there the blocage had cleared and it didn't do it anymore. While it was a problem, I just shut off the valves that control the slides when I put the jacks down and then turned them back on when I wanted to open the slides.
Dick, Joyce, Diego, Picatso and Gustav
2017 3720 RL, and 2013 HC 343RL
2017 3500 Dodge Maxi DRW 4X4, Pullrite Hitch, IS, Disk Brakes, 3rd AC, Winegard Traveler, Bathroom door mod, Dometic 320, couch for desk swap, etc.