Yes, it is definitely about skipping. It skips when it's too loose, not because the upper run is being pulled so hard - on the contrary, it's well seated. The lower run comes out of tension and that's where the skip happens. I had a belt-drive bike from Priority that started with a different non-Gates belt, with standard industrial teeth, and they sent me a Carbon Drive with the center ridge to test later on. The first one would definitely skip under hard effort, even at full tension, even though it had a snub pulley. The Gates version doesn't have a snub pulley and relies entirely on the tension, and on just being better quality. The center ridge has nothing to do with it, that is a dirt shedding feature compared to pulleys with sidewalls.

Gates know what they are doing. They make drive belts for all industries and some other things too like hoses. Not tires for whatever reason. I guarantee you don't know better than them. Their tension specs are higher for mid-drive and even higher for gearboxes because those put more and more tension on the belt.

I also found the app irritating to use. The value I got when I turned the adjusters would change entirely when I cinched down the axle. Fortunately the allowable range is broad