Distorted sprite on SpriteRenderer after changing material

Hello,

I'm trying to change my sprite to another material (using StencilMask as a shader) but as soon as I apply the other material (instead of the default SpriteDefault), my sprite is messed up.







The black one is my original sprite (the shape I need), the orange one (don't mind the color) is the distorted sprite once I applied my other material.

Here is my shader code if needed: https://pastebin.com/gBGG4ecj

Any idea what could be the issue?

Thank you very much!