The "()" lacing gap means that the person's waistline is resisting compression from the corset and pushing out at the waist, while the top and bottom are collapsing inward.
There are a couple of reasons why this might happen. The person may be naturally muscular or over-ambitious and they bought a too-curvy corset that their body is not ready for. There is a possibility, with patience and training, that they may be able to eventually close this corset comfortably.
However, most likely the corseter would be more comfortable starting with a less curvy corset.
There are risks to wearing your corset with this lacing gap. The steels that support the grommets are designed to remain straight, whether that's "||" or "\ /" or "/\". Whenever the bones are forced to bend or twist, like "()" or )(" or even in a "Y" shape, the distortion places an unnatural stress on the steel which may cause it to permanently bow, kink, or otherwise stay that way over time. If a steel gets accidentally warped, sometimes the only way to improve the situation is to swap out the bones.
A corset may also make this shape if the steels are too weak and wobbly to hold their shape. If one particularly muscular person experiences this shape with their corset, it's not a big deal, but if a corset brand notices many reports coming back of steels bending or bowing, they might want to consider upgrading their bones to a stronger type. You can learn more about correcting a bowed corset in this article.