I see that you have an outdoor kitchen. On my Sunset Trail with an outdoor kitchen, there are two air ducts are in the wall that goes between the bathroom and the outdoor kitchen. They do not connect to any ducting, they are just a pass-thru, presumably to provide ventilation to the outdoor kitchen refrigerator.
I do not have any heat ducts in the bathroom.
Is it possible that this is what you are looking at?
I almost never use my outdoor fridge without the door open, and I found that bugs come in these vents from outside, and cold air comes in in cold weather, so I blocked them.
Doug and Patience and Shelby the mutt
2015 Crossroads Sunset Trail Reserve ST26RB
2013 Ford F-150 3.5 EcoBoost XLT Supercab 4x4