RAX200 Custom DNS Not Work Occasionally

As you mentioned, in order for the intranet DNS service to work properly, the secondary DNS address cannot be set.

But this will cause a problem. If the DNS service of the intranet is abnormal, I cannot access the website on the Internet normally.

Generally, I set the primary DNS address to the IP address of the intranet DNS service, and the secondary DNS address to 8.8.8.8 or the DNS service address provided by the ISP, so that even if the intranet DNS service fails, I can still access the Internet normally.

Since my old Netgear devices don't have this problem, I still think it's a bug in the firmware of the RAX200 or even the RAXE500, so I opened a support ticket.

This post has a more detailed description of the problem: 

https://community.netgear.com/t5/Nighthawk-Routers-with-WiFi-6-AX/BUG-RAX200-always-chooses-a-random-access-between-the-domain/td-p/2213139