Resolved Sprite Resolver SetCategoryAndLabel not doing anything?

Any idea why this isn't working?

It doesn't throw any errors, and the category and label are correct.

I'm doing something similar to this elsewhere and that's working fine

Code (CSharp):

1. public UnityEngine.U2D.Animation.SpriteResolver eyesSpriteResolver;
2.  
3. void Start() {
4.  
5.    eyesSpriteResolver.SetCategoryAndLabel("Eyes", "Eyes03");
6.  
7. }