This problem (that obviously has nothing to do with the backlight) is called vertical banding and is quite extended on any OLED tv of whichever brand (since they are all produced by the same manufaturer). If limited does not impair the actual content viewing (by limited I mean with 5% or 10% grey uniformity pattern that you may find everywhere even on youtube).
Obviously it is also important to understand which view mode you select and which parameter have you (if) changed. I advise you to set personal that is the most accurate. Take a picture and repost it (with 5%, 10%, 20% at least)
