Strange behavior using PiHole / Brume MV1000 fw. 3.104

Hey everyone.

Been racking my brain over this for hours.

When I go into Advanced Settings, Custom DNS Server, then select the IP address of my PiHole, local network address 192.168.0.100, then enable, I get no DNS connectivity at all:

dig google.com

; <<>> DiG 9.10.6 <<>> google.com
;; global options: +cmd
;; connection timed out; no servers could be reached

When I try to force a connection to the DNS server, it gets a timeout:

dig google.com @192.168.0.100

; <<>> DiG 9.10.6 <<>> google.com @192.168.0.100
;; global options: +cmd
;; connection timed out; no servers could be reached

Then I turn off the custom DNS setting, and instantly can dig google.com both directly to my PiHole and also using the Brume:

dig google.com @192.168.0.100

; <<>> DiG 9.10.6 <<>> google.com @192.168.0.100
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31638
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;google.com.			IN	A

;; ANSWER SECTION:
google.com.		57	IN	A	172.217.168.238

I’ve tried every combination, both on the GL-iNet interface and in Luci to get this to work, but it kills the DNS on my network everytime.

Any ideas on what it could be?