Hello,
Oh I see, we did not add our loader here. On checkout page using default woocommerce loader, that added via woocommerce scripts.
You use latest theme version, so you need to update 8theme Core plugin (Appearance > Install Plugins). Also, I would recommend update all required plugins – http://xstore.helpscoutdocs.com/article/37-plugins-update
Let us know if you need any further assistance.
Regards
