Unable to access my GitLab fork

I forked gitlab-org/gitlab> to ctabin/gitlab> this week-end and could work on it without any problem (see !16715 (closed) and !16716 (closed)).

I tried to access it this morning and I get an error 404. Also, my merge requests are not accessible anymore (error 500). A git fetch gives me the error below:

rpc error: code = NotFound desc = GetRepoPath: not a git repository '/var/opt/gitlab/git-data/repositories/@hashed/28/16/2816f557ad664d68d806b4e47f1f33e326bf26bce8c71ec21d04e1602ba302c0.git' fatal: Could not read from remote repository.

In order to keep an up-to-date repository in ctabin/gitlab>, I configured to make a git pull on gitlab in the settings, which worked fine. Also, when I want to re-fork the GitLab project, it tells me that I already forked it, but leads me to the same 404 error.