When you round up the usual suspects, water is always at the top of the list. The first thing I would do is pierce one with a needle and see if there's water. Even if there's no water that doesn't mean it's not, but you might see it there. I had a 31fs. Examine closely the window above that area, along with the window seals and any caulking issue's. Look for cracks in the caulking. If you used a hose to wash it, it may be possible that the force of the water got past the seals. Next, climb the ladder, and examine the roof above that area. Look for any cracks in the caulking. While you there look for any cracks in the caulking over the entire roof. Another possibility is it could be a glue issue. If it's water, the best thing to do is cover it immediately to limit any further damage until you determine the cause. I didn't notice what year your rig is, but is it possible you don"t have the single pane windows? If not, the regular windows have drain slots that can become plugged and you need to clean them out. A hose can overpower those windows and set up a leak. OK I see you have a 2015 so you have the single pane windows.