There was a glitch in the system some time ago that caused this problem. Not sure if it ever got fixed.
It was a glitch that was available to mobile players a couple of years ago. It lasted two days before WGT fixed it for good. But there are some out there who chose to never play another ranked round since then, so their average remains the same. If they ever do play another ranked round, then it will make the adjustments that WGT programmed and their scoring average will reflect what it should be.