ok, thats "a new one for me" and here the result;
xxx@xxx-xxx:/opt/docker/pihole_v5$ getfacl /opt/docker/pihole_v5
getfacl: Removing leading '/' from absolute path names
# file: opt/docker/pihole_v5
# owner: root
# group: root
user::rwx
group::r-x
group:docker:rwx #effective:r-x
mask::r-x
other::r-x
default:user::rwx
default:group::r-x
default:group:docker:rwx
default:mask::rwx
default:other::r-x
Is this good or bad and what command should I run to fix it?
Did some fiddeling and couldn't find a working solution with ACL.
So I decided to "reset" ACL on the volume dir;
sudo setfacl -Rbn /opt/docker/pihole_v5/
This fixed it for me 
@juha thanks for helping!!