Remember, I've never and don't grow anything that could be considered full hydro (coco and perlite in a hempy application, along with organic soil are my gig), BUT! Every time I've seen that either the plant has been girdled and the wilting will progress to death, or something happened to a section of the root mass that feeds that part of the plant, or something happened lower down on the main stalk that feeds those sections of plants.
Remember, the xylem (very exterior 'bark' of the plant's stalks) is where all circulation occurs. When that has been violated circulation is cut off completely, thusly, stops. It can be like cutting an artery.