I installed Pihole Docker and it worked fine for a day.
Suddenly (after I made some changes to the whitelist and/or privacy settings) the Admin page was not reachable anymore and although DNS is still going through the Pihole, ads are no longer blocked. Restarting and reverting to the previous Pihole Docker release did not help. Also a reboot of the Raspberry Pi did not help.
The section in the diagnostics that I think is the problem is:
"*** [ DIAGNOSING ]: Pi-hole processes
[✗] lighttpd daemon is inactive
[✗] pihole-FTL daemon is inactive"
Debug token: https://tricorder.pi-hole.net/7pfbyo22pm
I now installed Pihole without Docker and it is working fine. Would be nice to run in Docker though.