Question Terrain Heightmap generation issue - results in sawtooth ridged terrain.

Images attached below of the issue I've been having. The terrain turns into a ridged, jagged mess when the height map is imported.

I've been processing in Illustrator, exporting as a png, and then converting from a PNG to Raw using Fiji (ImageJ). As far as I can tell the png (shown below) file is fine, as is the raw image. Everything looks fine until the terrain is generated from the heightmap. I imported the same heightmap (albeit the png) into blender and did not have any issue, but viewing both the heightmap and png - they are identical.

I've tried changing the byte order and depth, but changing either of those just results in a smaller jagged mess that looks nothing like the continents I'm trying to import.

This is one of the height maps I'm trying to import. I've added a gaussian blur in as well which did not help with the issue.