I suddenly started receiving the error in the subject line all day yesterday, and Cesium refused to load. Today it’s working again. If I changed defaultHeaders so that “Accept” was different, or not send the headers at all in source/Core/loadJson.js, it would start working. Did anything change?
You experienced some serverside throttling. Thanks for reporting this, I’ll have a look at the rules to see if they are too aggressive. We’ve experienced some unusual traffic recently and had to put some configuration in place to tame some abnormal traffic.
If you or any other users continue to experience issues, please let us know.