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re-opening gitlab-ce#45657

I'm trying official gitlab docker container 11.9.8-ee (c970180), but have encountered this issue again.

And by doing some inspect, the console revealed the following API v4 calls

For example:

/api/v4/projects/mygroup%2Fsample-project <-- this generates an {error: "404 Not Found"}

However, /api/v4/projects/ <-- provides JSON response containing details of all projects.