DNS_PROBE_FINISHED_NXDOMAIN for single website
I had the similar issue and was not able to open Facebook. Rest all sites were working fine. Initially, I thought Facebook blocked me as I never faced this crappy issue earlier. Later when I searched in Google, I found an article which described the DNS_PROBE_FINISHED_NXDOMAIN issue on Chrome.
I just changed my DNS server address as 8.8.8.8 (preferred) and 8.8.4.4 (alternate) and I never faced that issue again.
Reference - https://www.mobipicker.com/dns_probe_finished_nxdomain/
So from our discussion regarding the NS server records always make sure that the local NS records matches the Parent NS records.
In your case there there were 2 extra NS records associated with your domain that was the reason why your domains and sub domains were acting unhealthy. once you deleted those records the domains and sub domains were back to normal.