The issue I am facing:
My syslog contains a lot of messages like this:
systemd-networkd[1676]: eth0: Could not acquire DHCPv6 lease on NDisc request: Address already in use
As far as I can tell, it has no negative effects, but I wonder what's going on here. I'm running pi.hole on an Ubuntu 20.04 host, and I assume there's a conflict between systemd-networkd and dhpcd. I only found one link on the internet to help here, which recommended to deny dhcpd from managing eth0, but shouldn't I rather stop systemd-networkd from messing around with DHCPv6 somehow?
Details about my system:
Ubuntu 20.04.1
$ pihole -v
Pi-hole version is v5.1.2 (Latest: v5.1.2)
AdminLTE version is v5.1.1 (Latest: v5.1.1)
FTL version is v5.2 (Latest: v5.2)
What I have changed since installing Pi-hole:
Nothing 
This situation was there from day one.