That’s odd, I’m not able to reproduce this. What city/region are you making these requests from? Are you unable to access even Sentinel-2 (that comes directly from the Cesium ion servers) ? Have you tried creating a new token? What email do you use for this Cesium ion account?
Well, it’s quite weird, now it’s working, but on some tiles I still get the error.
I would seem to me a connection problem, but I don’t have any connection issue (with Mapbox tiles I never had any trouble).