This solution will walk you through the steps needed to fix the grid lines/ strips being spawned! 

The stripes are caused by the convexity/concavity mask - this mask uses a compute shader to calculate the convex/concave info by analyzing the surrounding terrain. When the terrain gets larger so that the spawner needs to iterate across it multiple times, you get the problem that the convex/concave mask fades out strength towards the edge of the spawner, resulting in those grid lines you are seeing.

This is difficult to fix for us in the application since this is more a logical problem in the underlying algorithm that calculates concavity. What you can do in the meantime is deactivate the convex/concave mask and replace them with a combination of height and slope masks instead. To do so, you need to look through the textures in the texture spawner and check where a convex/concave mask is used, take a look at the visualization, and then mimic the result with a combination of height and slope masks instead, for example:

here are the concave masks replaced with height and slope masks instead: