I mean, I said that an hour or so ago, but that was before the site had deployed... Turns out https://www.jvt.me/posts/2019/11/11/gotcha-netlify-lowercase/ caught me out again and isn't fixed until https://gitlab.com/jamietanna/jvt.me/merge_requests/638 is in (although I've done a temporary deploy from my local machine to get the site up).
Very annoying!