This probably might not be an issue with most other denims. The 19oz is very ridged and stiff and the area that thread broke is of a risky area for jeans that fit so close to the thigh and crotch area. Not a lot of give there especially with the stiffness of the 19oz. I’ve had this same issue with many high end jeans where i have tried to get away with a more fitted look. You can only expect so much out of a thread, even the most high end threads; it’s going to break under tension. Take for example fishing….. if you’ve lost a few fish, you know what i mean. My recommendation would be to put some fabric glue down where the stitch that broke or clear finger nail polish or super glue and it wont get any worse. Fabric glue being your best option. I can understand your frustration but don’t doubt this can happen to any high end denim or any high end garment in high tension areas where the fit is restrictive.
Hope this only helps. You can trust that it will be one of the few issues you will come across with those jeans you have there. I would just rock them and see what comes of them in a year or so. My bet; you will be happy as long as you are okay with the discomfort of a tighter fit until it loosens up for you. Which will take a long while with the 19oz
