Specific directory gets 404 on github pages

[gcarcassi]

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I have had website pages working for many many years. Today a specific subdirectory (obsviously the most important one with permalinks to the project) is no longer working. Anything inside that directory gets a 404 site not found:
https://assumptionsofphysics.org/book/index.html
https://assumptionsofphysics.org/book/AssumptionsOfPhysicsV3.0.pdf
What is weird is that links that are not on the webiste get a 404 FILE not found:
https://assumptionsofphysics.org/notexists
It's like that specific URL gets redirected somewhere else that doesn't exist. The tarball that publishes the website has the directory and all its contents:
https://github.com/assumptionsofphysics/assumptionsofphysics.github.io/actions/runs/22927316633#artifacts
The local build works. If I change the directory from book to book2 it does work... but, as I said, that's supposed to be a permalink. Other published documents refer to that link.

I already tried:
Rebuilding the site multiple times.
Unpublish the site from Setting/Pages
Went back and forth from Github actions and "standard" deployment

I really can't think of anything else... :-/ Ideas?

[gcarcassi]

I think I finally figured it out...

I inadvertently activated github pages on another repository with the same name (i.e. book), but the site was never built. So there was effectively a redirect to a site that never existed.