I've checked the website after building it locally, I've checked that github isn't having problems, I've checked it on other computers, in incognito mode etc, I've compared with other documentations created the same way as mine, github gives me no errors and yet I continue to get a 404 error at the website address.
Is it on a private repo? It seems that late last night a change went through with GitHub Pages on private repos being a paid feature. I have 60 students in panic mode right now - they used to be able to have this as part of the Student Developer Pack.
Unfortunately, no it's on a public repo and the issue has persisted since a little over a week ago.