DNS resolution for hhs.gov

I wanted to run this by everyone to make sure I am not the one losing my mind over this. A dig +trace cob.cms.hhs.gov fails for me as it looks like the NS for hhs.gov does not seem to resolve the hostname. However dig +trace cms.hhs.gov resolves and so does dig +trace eclkc.ohs.acf.hhs.gov However if I simply ask my local resolver to resolve cob.cms.hhs.gov, it works. Any thoughts on why this is the case? Thanks,