GitHub pages: 404 on / but / index.html works great

Question

my situation is this:

• I deployed the jekyll site for github using a docsfolder in the branchmaster
• It has an index index
• username.imtqy.com/repo/index.html works
• username.imtqy.com/repo/ returns 404

The site works well locally using jekyll serve(no 404).

I would expect GitHub to return the contents of index.html when receiving a request for a directory.

Maybe there is a problem with markdowns?