Steps to recreate:
Create an skeleton that uses skin placeholders. Add the same image (e.g. "head" )to more than one of the placeholders for a slot > Spine will automatically change to "head1", "head2" etc.
Open in Unity > Unity will complain that region "head1" doesn't exist.
Can be solved by clicking in the spine Hierarchy and manually deleting the numbers from the attachment names.
There were some issues with this but it was fixed a few weeks ago. Are you using the latest? I opened the goblins example, added a new skin placeholder to the "head" slot, put the same goblin head in it (tried both drag and drop and Set Parent), and I see the head image does not have a numeric suffix:
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Ive had a similar problem too and thats using 1.7.03, in my case I initially fixed mine by going into the json and correcting the name. But think was based on me manually renaming say head to head1, then adding in head again then renaming to head2 etc... rather than spine auto renaming. But the overall effect was the same.
