Hello AJoseph, I looked into the After Effects plugin, and the last time someone used it, they also got problems that varied from plugins possibly interfering with it, as well as invalid Json exports. After Effects to Spine

This export script was kindly made by a user, Nimai, several years ago, here you can find the detailed list of what is supported and what isn't:
After Effects and Photoshop export script for Spine

You can find the script also in the Spine scripts repository here: spine-scripts/aftereffects at master · EsotericSoftware/spine-scripts

I noticed that on that page it says:

If running the script from the ExtendScript Toolkit, ensure Do Not Break on Guarded Exceptions is checked under the Debug menu.

Could you try running it again as per instructions, and see if you still get the error?

By the way, if you're looking for resources to learn to use Spine, (in case this After Effects script problem might be blocking you longer than it should) I recommend also trying the PhotoshopToSpine script tutorial, which is maintained directly by us, and has a recently made tutorial video explaining how to use it:

As well as the user guide video series:

You can also find a beginner rigging tutorial which is suitable for ESS users:

And a long series of twitch streams with downloadable projects that cover a wide variety of cases:
Spine: Twitch