Displacement map only working on one axis

Hi everyone,

I am trying to set up a street corner scene using a curb I found on Sketch fab. The model only has a single colour PNG for the texture so I made my own displacement map buy taking that PNG and desaturating it and changing the contrast.

The problem is when I apply the displacement map it only seems to change the mesh on the X-axis and the Y axis just ends up as sort of bands of raised geometry.

I have put a subsurface modifier on the mesh and subdivided some of the faces a few times but it still has the same problem. The texture is a short panel that gets repeated again and again this might have something to do with the problem but I am not sure. I also had to skew the model to get mirror it diagonally that might also be causing the problem

I am including images of what the problem looks like, my node setup, the mesh in edit mode, my self made displacement map (lowered quality for uploading here), and the UV image editor for the displacement map

Here is a link to the sketch fab model Sidewalk - Download Free 3D model by FelixBDesign (@felix95b) [c4d846a] - Sketchfab

Any help with this would be greatly appriciated ,

Thank you,