@alephZero, did you happen to check pinned comment and try?
Checking /etc/shadow, the user http had a trailing 1:
$ sudo cat /etc/shadow | grep http http:!!:18174::::::1: Removing the expiration date has resolved it:
$ sudo chage --expiredate -1 http
Pinned Comments
max.bra commented on 2018-02-09 16:45 (UTC) (edited on 2019-10-18 23:14 (UTC) by max.bra)
ArchLinux Pi-hole is not officially supported by Pi-hole project. In case of bugs and malfunctions please DO NOT file a report upstream.
First of all check if the wiki (https://wiki.archlinux.org/index.php/Pi-hole) can help then ask here for assistance and tips.
When it will be excluded that the problem does not depend on ArchLinux we will file a bug upstream.