I should probably do some major overhaul of my character, but for now, fixing this is first.
I have a player character as a prefab and updated it via versioning system.
What changed was all the spineUnity scripts(ie: skeletonAnimator) were unlinked from the prefab's components.
I've manually put them back to the broken prefab, however, unity still yells at me saying: The associated script cannot be loaded. I then checked through character data files and found file Player atlas_Atlas file was the only different thing than the working original prefab. Where working prefab's atlas_Atlas has 'atlas.atlas.txt' connected the broken one has 'AtlasAsset' script from Spine-unity Asset Types folder, and I cannot re-link the atlas.atlas.txt to it.
My Unity version is 5.6.0f3