I've no idea why it wasn't working for some people, although I very much knew what caused the issue.
I tested the changes myself on Mac, iPad and iPhone and the site was fine and continued to be when others were having troubles. Apple users, particularly on phones and tablets, dominate NSC...
I've just backed out all the ad changes so we're as we were. It should work for everyone again (although I've got no idea why it wasn't working for some).
Yesterday I reinstated an ad network that we used to use so it's sure to be related to that, although it shouldn't be.
Is it just affecting Safari on iPads?