Several times I see in my log that the automatic gravity update on Sunday 1’59" gives a Status 000 (List download failed, using cached list (list not updated!)) error.
The cause for this that in a time zone all PiHoles, located in that time zone, access the webservers, mentioned in the adlist at the same time (exact the same minute !!!). And weak servers (f.i. zeustracker.abuse.ch) cannot handle more then 1000 requests for the block-file.
I have solved this by changing the time (only minutes) manually and after that no problems like this.
Is it possible that when the Pihole is updated (pihole -up), the cron task pihole gets a random time for the minutes by the PiHole -up process? Thus in every update process a new random time (only minutes) is stored in the pihole cron task. Advantage is that all PiHole have a different time for running the automatic gravity process