I'm experiencing the same issue when loading listing configuration page(s) For me, this has been in conjunction with the issue I (and others) detail here: There's been no answers in that thread either, but it might be worth watching. You may want to try synchronizing site data, to see whether or not we're all having the same problem.
I'm in the same boat. Persistent alert of: "Australia data was changed on eBay. You need to resynchronize the marketplace(s) to correctly associate your products with eBay catalog. Please go to eBay, Amazon, Walmart > eBay > Configuration > eBay Sites and press Update All Now." When attempting to update, met with error Route ""adminhtml_general/synchCheckState" not found" One of my main categories has been changed by eBay and I'm now unable to update/sync. The failed updates had been occurring for at least several days prior to upgrading the plugin. Would love some guidance on this issue and it looks like I'm not alone!