@Midial Sorry to hear you're having troubles. Please note that the 4.1 unitypackage you're using (2024-02-26) is not the latest available (2024-06-19). When encountering issues, please always check first whether the latest package fixes your issue:
https://esotericsoftware.com/spine-unity-download#Older-Versions
If it does not resolve the issue:
My best guess for your above out-of-range array access to happen is if the loaded (binary) skeleton format does not match your spine-unity runtime version. So i.e. the exported skeleton data file is of an older or newer version than your runtime supports. Have you perhaps modified the spine-unity runtime code, and i.e. changed any of the version checks?
If you can't reproduce this issue locally, are you perhaps using any download mechanism like Addressables, Asset Bundles or the like? If so, please make sure that there are no outdated download packages left which might be loaded accidentally instead of the correct package.
