This is quite rare - the C root-servers are out of sync with the rest of the world by 3 days. Since that time there have been no changes in the root zone, except for DNSSEC signature updates. It appears all C instances (operated by #cogent) are serving an outdated zone. For now this has no operational impact, but that might change #DNSSEC - UPDATE, c-root received an update and now only lags behind by 1 day now. UPDATE2: fixed.