Impossible to push on some repo, remote: GitLab: API is not accessible

I have forked Gitlab CE on a personal repo years ago. In the last 3 months I wasn't able to keep it up to date, so last commit on master (taken from upstream) is on the 9th of May.

Today I updated my local copy with upstream changes, and when I tried to push them to my repo, it failed without any useful error:

gitlab/gitlab-development-kit/gitlab  master ✔                            12m  
▶ git push origin master
Counting objects: 50755, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (19878/19878), done.
Writing objects: 100% (50755/50755), 15.57 MiB | 4.25 MiB/s, done.
Total 50755 (delta 38375), reused 42382 (delta 30308)
remote: Resolving deltas: 100% (38375/38375), completed with 2870 local objects.
remote: GitLab: API is not accessible
To gitlab.com:rpadovani/gitlab-ce.git
 ! [remote rejected]         master -> master (pre-receive hook declined)
error: failed to push some refs to 'git@gitlab.com:rpadovani/gitlab-ce.git'

Both my local master branch and online forked master branch are clean, and to not have any custom commit.

I do not have any protected branch, nor any push rule.

I wasn't able to reproduce on any other repo, and my account works just fine.