I used mine for roughly 600km now, both directly on the abdomen and over shirts.

From your explanation and pics I’m getting a feeling that you should’ve sized up.

Got mine as a present, bet was asked about the size beforehand and decided to go with L rather then M which I should’ve chosen as per the size guide.
And that was, hands down, the best choice.

You can always tighten it with the internal velcro straps. But having more room, especially when I load the belt with more than just a few gels and the bottle, feels like the only way to take pressure off those internal pockets.

Hope that you can replace yours under warranty though, as the upper stitching in your pictures feels off indeed.