Hey Harald and everyone 
Posted a bug ticket here: https://github.com/EsotericSoftware/spine-runtimes/issues/2110
This error is only happening for me when I select a specific Root Motion Bone.
Thanks!
[4.1 Bug] SkeletonRootMotion index error
- Изменено
Sorry for the trouble! Thanks very much for reporting and finding the cause of the problem already, much appreciated! 
A bugfix of the spine-unity runtime is available on both 4.1 and 4.2-beta branches, available for download here as usual:
spine-unity Download
Harald написалSorry for the trouble! Thanks very much for reporting and finding the cause of the problem already, much appreciated!
A bugfix of the spine-unity runtime is available on both 4.1 and 4.2-beta branches, available for download here as usual:
spine-unity Download
Hey Harald! Thanks for the quick reply - unfortunately the bug is still persisting for me
I updated the bug ticket with more info, and uploaded the spine character that I'm using to test it out, in case that helps.
Thanks for the help!
Harald updated the issue ticket and fixed the issue. Thanks a ton!!