This is just for visibility. It took me days to get this resolve. My OMV suddenly stop resolving. Basically, I couldn't install new Docker Containers, I couldn't update the OMV os, as al repositories were 'Unreachable'.
After days of digging into it, this can be fixed as easy as running this command:
systemctl restart systemd-resolved
I don't know if this is documented, but It could be great to have it somewhere for further users with same issue: OMV unable to resolve Hosts (lack dns).
Issue is resolve not, I wanted to create this post for further users with same issue. It drove me mad until I figured out how to solve this.