It’s because of the subdivision surface and the creasing you’re using to control it. It would look better without cutting the edges but still, it needs supporting loops
Left: creasing, sharp edges. Right: support loops
You didn’t provide an example .blend. Do that in the future, tutorial linked in my signature shows how and where. You managed to get enough information visible in the screenshots this time by not cropping them, but still slowing down replying to you, and hiding all other information that might be relevant to the problem.