Pi-hole returns strange fqdn for itself

When I do a reverse DNS query for the ip-address of pi-hole itself I do get a strange answer.

I use knot-resolver as my backend resolver and if I ask knot, I get "pi-hole.example.com."
But if I ask pi-hole I get "pi-hole.no_fqdn_available."

Where is that name coming from? And why?

I do not use pi-hole as my dhcp server, but knot will ask my dhcp server for reverse queries and get the correct answer.

Please upload a debug log and post just the token URL that is generated after the log is uploaded by running the following command from the Pi-hole host terminal:

pihole -d

or do it through the Web interface:

Tools > Generate Debug Log

https://tricorder.pi-hole.net/NphWBvBR/