I have installed Pi-hole less then 24 hours ago and now I see the error message mentioned on the topic subject.
The strange thing is that everything seems to be working fine in terms of the DNS, i can still look at the log and that requests going normally.
What is not working is once i login to the admin i see that it shows me "dns service is not running" and there are no logs
If DNS and blocking are working then I would suspect a default firewall rule is preventing the web admin console from interacting with FTL on port 4711. This isn't a supported system though so you may have experiment or reach out to the script maintainer for assistance.