Cannot delete a project

I cannot delete one of my projects on GitLab.com: here it is, project ID 29462565. I got an error yesterday explaining that there were build artifacts that couldn't be deleted, but the artifacts page is desperately empty! Today, the error message does not appear anymore but I still cannot delete the project.

Here is a screenshot of the artifacts page showing no artifact, but a non-zero "Total artifacts size". I'm wondering if the problem is related to that:

Thanks in advance for your support.