They never hooked up the valve under the sink on my 2017 Jayco. Poor quality control. Very strange that the valve turns water off to your sink. Almost like they just hooked it up wrong. Maybe they have new crop of workers on the assembly line? Agree with Klassic, open low point drain under kitchen slide. If water is coming out then you have fridge problem. Also, when water wasn't going to fridge, every time we tried dispensing water the valve/pump was loud. Once I got water flowing to it you could not here it anymore. They way I got water to it was to run a 1/2" hose to the kitchen slide outside. I cut the garden hose line under the slide, and splice the 1/2" hose into that line(The part of it going towards the outside of the slide) by using a 1/2" brass splice connector. Had to get a splitter with more then 2 outlets to put by water center. I now have 3 lines there, one for city, one for tank flush and one for fridge. Kind of a pain, but unlike you we do not move our trailer, it's parked in a seasonal campground so not really i big deal to have it hooked up the way I do. Will actually make it easier to winterized as well.
See the link below to follow what I did to troubleshoot etc. with pictures..
Good Luck! And if you have any questions let me know.
Link to connector I used