Norton ConnectSafe DNS issue with Fios Quantum Gateway G1100

Recently, I started having issues accessing the https://my.t-mobile.com/ site. For example, my Google Chrome browser displays the following errors:

Your connection is not private
Attackers might be trying to steal your information from my.t-mobile.com (for example, passwords, messages, or credit cards). NET::ERR_CERT_COMMON_NAME_INVALID
This server could not prove that it is my.t-mobile.com; its security certificate is from search.dnsadvantage.com. This may be caused by a misconfiguration or an attacker intercepting your connection.

My G1100 broadband connection's DNS Servers are configured to use Norton ConnectSafe (see https://dns.norton.com/). I had followed the instructions at https://www.verizon.com/support/consumer/internet/opt-out-of-dns-assist/fios-quantum-gateway to configure my G1100 with ConnectSafe's IP addresses 199.85.126.20 and 199.85.127.20.

When configured to use ConnectSafe, my G1100 returns the following incorrect IP addresses for my.t-mobile.com: 156.154.175.216 and 156.154.176.216

What's even more disturbing, is that those returned IP addresses do not appear to come from the ConnectSafe servers. If I query the ConnectSafe servers directly for the IP address of my.t-mobile.com, the 199.85.126.20 server returns 199.83.128.144 and the 199.85.127.20 server returns 192.230.66.144. On Windows, I queried the servers using the "nslookup my.t-mobile.com 199.85.126.20" and "nslookup my.t-mobile.com 199.85.127.20" commands. On Linux, I queried the servers using the "dig my.t-mobile.com @199.85.126.20" and "dig my.t-mobile.com @199.85.127.20" commands.

I have a Netgear router in my network. If I configure my Netgear router to use ConnectSafe, my Netgear router returns the 192.230.66.144 IP address and I'm able to access the https://my.t-mobile.com/ site without issues. This makes me think the issue is with my G1100.

If I configure my G1100 to use either Google's servers (8.8.8.8 and 8.8.8.4) or OpenDNS's servers (208.67.222.222 and 208.67.220.220), the G1100 returns the 199.83.128.144 IP address and I'm able to access the https://my.t-mobile.com/ site without issues. It seems that my G1100 has issues only with the ConnectSafe servers.

I did notice that Google's servers and OpenDNS's servers respond to pings whereas the ConnectSafe servers do not respond to pings, but I don't know why that would matter to the G1100.

By the way, my G1100 has firmware version 1.3.0.47.64.

Does anybody have any idea why the G1100 has issues with the ConnectSafe DNS servers?