Hmmm I suspect that you should submit a bug report with your project as it should work from 3.4.02 (that is what we are using internally) - let us take a look at what is going on.
Russell
Ok! working in 3.5, but i think the issue is related with Spine project, after updating Spine, first you must have :
1 - Open the project with new version.
2 - Save the project with new version. (An advertisement is showed telling you can not revert the progress for older versions).
3 - Close Spine and re-open this.
4 - Export the asset.
EDIT : Very happy, you have fixed the memory leak with skeleton bone states!