Mesh triplanar normal mapping issue

Hi folks, I'm working on a marching cubes voxel terrain, for this I have created a simple triplanar shader on Shadergraph with normal mapping however this normal mapping doesn't appear to work on the X axis of my terrain, I've included the sphere below with the same material applied to show the normal mapping as it should be. I've also displayed the normal directions to show that the mesh at least appears to have this set correctly.



I manually re-pointed all of the normals to -x to show the issue more clearly with a plane for comparison.



This also appears to happen on cg shaders on SRP so it's definitely not limited to Shadergraph, does anybody have any idea what this issue could be?