I replaced the valve cores on the front and back of my gravel bike which came with the stock specialized cores. For some reason the one on the back leet in my tire was flat. I tried a few things and nothing helped. Since the package came with six. I replaced it with a new one and it held air. That seems to tell me that the one I used it first was defective. So far I've used three of them and one of the three was defective.
