Using internet root servers.  But the issue hasn't been seen again since March 29th, so whatever was returning the wrong values appears now to have updated.

We currently have this too.  Checking from cli we usually find either no value returned for nslookup of v2.sds.cisco.com, or a value which differs from that which we get when checking it directly.  dnsflush, after which nslookup gives the correct val...