Hi, I've found what appears to be a bug in the latest version of Unity and the Spine unitypackage version.
I copied the dragon.png dragon2.png dragon.json and dragon.atlas.txt file into another folder from the examples folder. It generates the atlas and material files correctly but no SkeletonData file.
Is this a known issue? Is it because of it using multiple textures in a single atlas?
I found this bug while trying to import my own animation which also failed silently so I tried it with the dragon example and found the same issue.
Unity 5.6.2f1
spine-unity-3_6-2017-06-24.unitypackage
Cheers,
Daniel