I did a bit of googling on how to remove scenary cache and found theres rolling cache and manual cache. I deleted the rolling cache but the terrain split is still there. I dont have any option for manual cache in FS. Which suggests that I never set it up right?
My next idea is to try and repair the game files. So I did a ‘verify the game files’ in the steam properties options. This forces FS to re-download all the packages next time you start. So now just waiting for 26Gb to be downloaded. Dont know if it will fix it. Fingers crossed.