I had this issue and the culprit turned out to be that I had created a repo just before with the same name and then deleted it. When I renamed the repo of interest the live page loaded up just fine.
I have the same problem that a lot of people are having, but don't see how it is getting fixed.
I was hoping to use the address <username>.github,io,
I first tried creating the pages in a repository called /docs, but under settings -> GitHub pages -> Source,
the option to use docs as the source was greyed out. Then I tried creating a repository
<username>.github.io, and when I do that, under settings -> GitHub pages -> Source, rather than
giving me a menu, it says that "Your GitHub Pages site is currently being built from the master branch"
and above that it says "Your site is ready to be published at http://<username>.github.io/"
Sounds good, but when I click that link I get a 404 page. I'm sure I'm missing something
(maybe "ready to be published" is different that "published" and I need to do something else),
but I don't know what.
I assume you were able to push the code successfully to the repo.
Make sure the following things are in place:
1. Angular Cli Version should be 8+.
2. Repo should be public and not private - navigate to settings and change the repo to public.
3. Try the following command: ng deploy --repo=https://github.com/<userID>/<repoName> --base-href=https://<userID>.github.io/<repoName>/
In the settings page, you'll get the generated link.
Check the network tab to see if the bundles are being loaded successfully, else clear the cache once and try : ctrl + shift + R.