Cannot fork a project after already forking and deleting

I cannot fork a project of mine. I did successfully fork it once. Then I deleted the fork.

Now I can't fork it anymore. By clicking the "Forks" button, which shows a count of 0, the project homepage reloads. By manually constructing a link to the forking workflow page, then clicking the blue "Fork" button, the project homepage reloads.

The project homepage in question is: https://gitlab.com/kevindoughty/history