Aha, that is much more info, thanks! 🙂
Can you try this:
1) Make sure your Spine is at version 1.3.26 (click the menu in the upper left to see the version).
2) Export your animations again using 1.3.26.
3) Update spine-libgdx to the latest. You can update using git or download all the source using the ZIP button on github.
I think it will work after that. There was a change recently to add the ability to disable inheriting rotation and scale, and also for additive blending on slots. This didn't affect the JSON format, since it uses named attributes, but the binary format is more susceptible to changes. In this case, the extra fields mean you need to export your animations again using the latest Spine and also use the latest spine-libgdx to load them. Sorry! This only happens if something in the export format changes. Most updates won't change the export format.
Note the .spine project file format will always handle forward compatibility, meaning the latest editor will always open older project files, though an older editor may not be able to open newer project files. The export format does not guarantee forward compatibility because this format is consumed by lots of different code and the compatibility would complicate the format. Hopefully it isn't too bad to export your data from Spine again.
If you don't want to be affected by this, you can disable automatic updates in the Spine settings and be sure not to update spine-libgdx. The downside to doing this is that you won't be able to use new features.