Radeon Pro 560 memory maxing out

I have installed the iStat menus app on my MacBook Pro 2017 to check performance as I was getting some stuttering/lag running a game (not really graphic intensive game either) and found that the memory usage of the Radeon Pro 560x is maxing out at 100%

The GPU processor usage is very low but the memory is full and getting close to 75% just doing basic tasks..

Anyone else seen this?, as it appears that the GPU/macOS is not releasing the memory so just exhausts at 100% eventually even when tasks has finished, which points to a macOS driver issue possibly but couldn't find any info on last update to see if that has caused it.