Honestly this is a duplicate of Use cached adlists on startup to improve startup times - #2 by jfb
Basically, why can't we have an option to remove this load on startup of the Docket container...? no need for a log there... just try and reboot a pihole Docker image.
Having additional blocklists to the defaults is common, and having to reload them on start is useless if I am for example rebooting my machine for testing changes or whatever. This process costs 20 seconds on my machine, in which time I have no DNS. We could have an opt-in option for that...
Using PiHole as a primary and only DNS and having to wait until the lists are loaded to have the DNS service up is a bit mess.