I have a (very barren) site deployed at compassionate-feynman-1e69e9.netlify.app.
If you click the link, it will display the index page without CSS applied. A click on a page link, either the one page or the link back to root, will append
main-- to the front of the address and css will be loaded properly. Also a direct link to
main--compassionate-feynman-1e69e9.netlify.app will display properly. BTW, main is my deploy branch.
I had another netlify deploy that was acting this way until I changed over to a custom domain and added
netlify.toml to the root. The
netlify.toml was essentially a copy of https://github.com/gohugoio/hugo/blob/master/docs/netlify.toml with updates to the hugo version that I am running. Adding this same file to compassionate-feynman-1e69e9.netlify.app failed the deploy.
Github repo is public if that helps. https://github.com/zjeaton/hugo-demo-site