I am using the latest version of Spine with Unity 2019.3 and there seems to be a bug when applying PMA while cloning sprite attachments.
This is due to the way Spine implements
Graphics.CopyTextureif it is supported which may or may not finish before calling
Texture2D.Applywhich is used to apply PMA - according to the Unity docs:
"Calling Texture2D.Apply, Texture2DArray.Apply or Texture3D.Apply after CopyTexture yields undefined results as CopyTexture operates on GPU-side data exclusively, whereas Apply transfers data from CPU to GPU-side."
I would recommend adding a flag to
AtlasUtilitiesso that the PMA can be applied directly during the copy and if the flag is not set go ahead and use the optimized