Update:
Found that raspberry pi is scheduled through cron to restart Saturdays at 04:00. That brought me to a similar issue: Pi-hole stops working after power outage or restart.
In that thread it is suggested to restart pihole and selecting repair, did that and it for now looks to have solved the issue. New debug token:
https://tricorder.pi-hole.net/BUn7hHRP.
It being related to the scheduled restart of the raspberry pi at least explains the intermittency of the issue. However why it would usually start working after the weekends again I’m not sure about. Related to pihole gravity update maybe?
And in addition to that, why does pihole appear to consistently malfunction after a raspberry pi restart?