If your skeleton is drawing from multiple textures, there is a known bug in Unity 5.6 and above where Unity's sorting system sees common materials between instances and tries to batch them, but breaks the sorting in the process.
The fix in that case is to add a Sorting Group
component to each instance.
A fix that has better performance scaling is to make sure your skeleton is only using one texture. This also makes it so that the Sorting Group is not required.
If this isn't your problem, can you describe your setup more?
Technically, this is not zfighting, as z-fighting is specifically a depth buffer accuracy problem: https://en.wikipedia.org/wiki/Z-fighting