3D pixel art shader only sharp when square resolution

This is difficult to explain, but I have this image that is 15x16, but when I import in to unity it appears warped and blurry.

Original image:

How it appears in-game:

I am familiar with this issue around pixel art, but the filter mode is set to point and the compression is turned off. The image is shown through an unlit URP shader, but I have tried other shaders and even a custom texture shader. Oddly enough, when the image is a perfect square such as 16x16, the issue completely disappears and the texture appears sharp as normal.

Are you sure that this is shader related? By default, unity rounds up texture sizes to powers of 2, you can try to disable that in the texture import settings.