Pihole 6 Beta resolve.conf receives a IPv6 FD Address

Hello community,
I am running the Pihole 6 beta on a Raspberry Pi 3 and for some strange reason the resolve.conf keeps receiving a IPv6 FD Address

Does anybody have a clue, what the reason for this irritating issue could be ?
Thx,user4747

Likely, your router is advertising its own IPv6 address as DNS server, allowing your clients to by-pass Pi-hole.

You'd have to find a way to configure your router to advertise your Pi-hole host machine's IPv6 as DNS server or to stop advertising its own.

You'd have to consult your router's documentation sources on further details for its IPv6 configuration options.