It seems like I tricked gitlab in a kind of transient state.
I want to rename (changing path of) a project. If I try to do that I get a HTTP 500 error. If I instead try to create a new project under the desired name I get this error in the GUI:
The form contains the following error:
Name has already been taken
I guess I confused gitlab somehow. Maybe an admin can look at it in the backend and fix it for me?