Underlay not working with Custom Font

Hi there!

So our artist has made his own custom font, and we've used the font asset creator to get it in unity.

For whatever reason, the "Underlay" option doesnt seem to do anything for these custom fonts. Its not that the option doesnt appear, it does, its just that no matter what parameter I adjust (dilate, softness, color, offsets, etc..) nothing happens to the text at all.

Also we're not using any special shaders, this is with the TextMeshPro/Distance Field shader.

Any help would be greatly appreciated!

Thanks!