Let's go a lil'more 'lower level':
Can you SSH into your Mango? There's a piece of software we can run from the command line called drill. It's used to troubleshoot DNS resolution. That this problem is only happening on the Mango is quite something else. I'd like to chk what's going on w/ the Mango's DNS service.
opkg update; opkg install drilldrill +short $yourAsusDDNS
Example:
root@flint:~# drill +short quad9.net
;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 46273
;; flags: qr rd ra ; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;; quad9.net. IN A
;; ANSWER SECTION:
quad9.net. 2390 IN A 216.21.3.77
;; AUTHORITY SECTION:
;; ADDITIONAL SECTION:
;; Query time: 0 msec
;; EDNS: version 0; flags: ; udp: 1232
;; SERVER: 127.0.0.1
;; WHEN: Thu Nov 30 17:01:30 2023
;; MSG SIZE rcvd: 54
See the link below. The default IP for GL devices is 192.168.8.1, username root.