ASUS still has same "design flaw" in their new ZenWiFi AX TX8 mesh routers... 
The problem is that You have to disable the probing on each node, one by one to get rid of the problem.
Here is how:
https://www.snbforums.com/threads/constant-unwanted-traffic-to-dns-msftncsi-com-from-rt-ac66u.35367/
Or in short:
- 1 - Enable SSH (or telnet).
- 2 - SSH into your router and each node one by one
(login & pw is the the same as your web interface) - 3 - We're going to change the NVRAM settings but its worth having a look at the default first so do a:
nvram show | sort | more - 4 - Look for: the dns_probe_content and dns_probe_host entries. These have the addresses that were giving me the problem
- 5 - Set dns_probe_content using:
nvram set dns_probe_content=127.0.0.1 - 6 - Set dns_probe_host using:
nvram set dns_probe_host=""(note "" = null, ie blank, ie not even a space) - 7 - Save these entries:
nvram commit - 8 - reboot the router/node:
reboot