Issue filter/search not working on GitLab.com

Summary

On the new issue search/filter, when typing Label and clicking on the label item, the list of available labels is not shown as the resource is 404'ing

GET https://gitlab.com/gitlab-org/gitlab-ee/issues/labels.json 404 (Not Found)

Steps to reproduce

• Open https://gitlab.com/gitlab-org/gitlab-ee/issues/
• Type "labe"
• Click on label:

Expected behavior

Should see a list of available labels

Actual behavior

Nothing, just a spinner and you will witness an error in your JS console: GET https://gitlab.com/gitlab-org/gitlab-ee/issues/labels.json 404 (Not Found)

The same happens with other the milestone resource, author and assignee appear to be working correctly.

Output of checks

This bug happens on GitLab.com