DNS Lookups to dns.nextdns.io fail

When using NextDNS IPs 45.90.28.234 and 45.90.30.234 the command "nslookup dns.nextdns.io" (or nslookup dns.nextdns.io 45.90.30.234 -or- nslookup dns.nextdns.io 45.90.28.234) return address 0.0.0.0. If I use another dns server like Google DNS (eg., nslookup dns.nextdns.io 8.8.8.8) the hostname steering.nextdns.io with several IPs (like 45.77.162.235 and 162.250.2.3) are returned.

I can use the DNS servers on my internal hosts and name resolution works fine. The issue is secure DNS using the string in my browser settings or the filters on client side (iOS, IPadOS, MacOS) fail. If I disconnect from my network and use cellular the same filters work. Seems to be a name resolution issue for dns.nextdns.io.

If anyone has any guidance (besides "why are you using NextDNS", I would use ...) that would be great.