I do not have your chairs so no direct help.
When we were at a dealer looking at new campers, we tried the chairs and one did not work. the dealer stated sometimes this happens and they have to disconnect the cord at the chair itself, and not the wall. I suspect it is a loose connection issue. May also want to swap power supplies at the same time, to verify if it is the chair or the power supply unit. FYI, the chairs we saw, had what looked like laptop power supplies.
Hope this helps
2012 Jayco X23B
2020 Ram Laramie 3500 SRW Air ride 50Gal fuel tank.
2007 Dodge Dakota Quad Cab (retired from towing)
Equal-I-zer 4-Point Sway Control