GitLab issues is still shown with Custom Issue Tracker service
As you can see from the link below GitLab Issues is still accessible. This is to be expected actually, if I disable Issues there is no "Issues" link on the project page.
Even though I can create issues, I cannot close issues after their creation. This is tested with both GitLab API from a third party application on my Android device and from the web interface.
Attempts to close issues with comments leaves the comment, but does not close the issue. These issues can be assigned to contributors as well.