Has GM updated to 3.4 yet? They should be able to tell you, as they are the ones who integrate the Spine Runtimes with GM. I saw they said on Twitter they were working on it, but I don't know if they finished. If they only support an older Spine version, you may be able to export to JSON and import into an older Spine, or wait for GM. We'll be up to 3.5 soon, so GM will have to update again (it's never ending! 🙂). Careful not to update to 3.5 before GM is ready.
You can try your animation in the Skeleton Viewer:
Skeleton Viewer
If it doesn't work correctly there, then it is likely our problem and we will fix it ASAP if you provide the .spine file so we can see the problem. If it does work there, then it may still be our fault if its a bug in the particular runtime being used (GM uses different runtimes based on the deployment target, eg spine-ts for browsers, spine-c for desktop, etc) or it's a bug with how GM has integrated the runtime, in which case they can help you.
