It is still common, however, that UX professionals consider that their work is finished when developers begin to build the product that was designed. Perhaps by inheritance from waterfall (cascade) methodologies, where the work of one area ends when deliverables are passed to the next area (as in an industrial production line). But even when the product is already 100% implemented, the work of UX is not yet finished.
Keep in mind the meaning of UX: User experience
If the user clicks a button that does not work, this will cause a problem in the user experience. Similarly, if the user clicks a button that does not work the way they expect it to, this will also cause a problem in the user experience.