Repro steps:
1) Create new Skeleton Animation in a new scene
2) Set the new Skeleton Animation's material to use the Spine/Skeleton shader
3) Set the material's Stencil Comparison to LessEqual (skeleton animation will disappear if placed in a new scene)
4) Switch the material to use Spine/Sprite/Unlit
5) Skeleton/Material seems to retain the LessEqual value, without an option to change it on the Spine/Sprite/Unlit parameters list.
Highly possible that I'm missing something, but couldn't figure it out. If I go back to the Spine/Skeleton and switch it back to Always (skeleton becomes visible), and then switch back to Spine/Sprite/Unlit, it remains visible.
The Skeleton Animation's Mask Interaction setting is set to None.
Also, is there a reason the Stencil Comparison setting is [HideInInspector] for the Spine/Sprite/Unlit? Is it because its supposed to derive from the Skeleton Animations "Mask Interaction" setting?