Hmm... that is pretty odd.
Though this could just be your png and atlas files being out of sync.
When you export an atlas from Spine, it packs the images into one texture. And the information of where those individual images are is stored in the .atlas file (.atlas.txt
for Unity).
If it was packed a few times because you added or removed images, the images will have been rearranged by the texture packer.
So if you used a new texture and an old atlas file, or an old texture and a new atlas file, it the information in the atlas will be incorrect.
To remedy it, make sure when you update the texture, you also update the atlas file. Also make sure there's only one. You may have both .atlas. and .atlas.txt files in your project folder, which can make things ambiguous for the editor regarding properly updating the correct file.
You can double-check the export settings here: https://github.com/pharan/spine-unity-docs/blob/master/Export-Settings.md
We haven't seen any users report something like this before but I assume this is the likeliest thing that's happening.
If that's not the problem, we may have to track down what's going on further.