PTR requests not sent to the router

[diasdmhub]

AdGuard v0.107.53

I have a router that provides DHCP addresses and local DNS names.
Each DNS record has a PTR address, so I've set the AdGuard "arpa" domain upstream server and the "Private reverse DNS servers" to the router.

Upstream DNS servers

# Local DNS server
[/in-addr.arpa/]192.168.8.1 fd01:192:168:8::1
[/ip6.arpa/]192.168.8.1 fd01:192:168:8::1
[//]192.168.8.1 fd01:192:168:8::1

Private reverse DNS servers

192.168.8.1
fd01:192:168:8::1

Whenever I try to query AdGuard for a PTR record, it fails to find the answer and responds with "NXDOMAIN".

$ dig @192.168.8.5 PTR 192.168.8.11
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 33857

;; QUESTION SECTION:
;192.168.8.11.			IN	PTR

;; Query time: 23 msec
;; SERVER: 192.168.8.5#53(192.168.8.5) (UDP)

When I track queries in AdGuard interface, I can see that it receives the request and sends it to an external DNS server, not to the router.

So, I'm not sure why AdGuard is not sending requests to the router.
Any thoughts on this matter?