All LED tvs even 4K especially over 65+ will exhibit vertical banding to some degree. You can exchange tvs a dozen times and you will still wind up with at least minor vertical banding. Even the LG $15,000 4K exhibits noticeable vertical banding. Considering the x900a 4K sets use the LG panels as well, it will be of no surprise as owners start to mention seeing minor vertical banding on those as well.
If you only see the minor banding on panning shots like hockey or soccer for example...I can tell you right now you are not going to get/find one with less.
If you see noticeable vertical banding at all times, than it may be an issue and an exchange may be warranted.
But to expect to get any LED 65+ with zero noticeable vertical banding is not a realistic expectation as it does not exist. Some owners may not be as sensitive to it or have a good enough eye to spot it.... but it is there.