JFB, thanks for responding.
Here is the page that I found that recommended use of "lan.list"...
As you can see, it is listed here, on this very site. Having established that this is bad advice - and for anyone else who make come to this conversation in future - can you recommend the best way to fix this? Would it simply be a case of manually adding my intended DNS entries via the web GUI and then deleting the "lan.list" file from the /etc/pihole folder? (I did create the file in the first place, so your comment "Don't make changes to this file" is slightly confusing in that regard. Is it safe to delete? Or should I delete it and then "touch" it back into existence? Or something else?
Perhaps if you could lay out your recommendation as a couple of simple steps that would help others to follow.
Thank you
... and maybe, as a moderator... you might have the ability to deprecate, edit or remove the above post with the bad advice?