### Summary Opening a milestone from the parent group milestones view returns 404 Not Found page. ### Steps to reproduce * Create a top-level group * Create a subgroup * Create a milestone for the subgroup * Navigate to the top-level group milestones screen * Click on the milestone from the subgroup * Instead of the milestone, you get 404 Not Found page. * Go back to the top-level group milestones screen * Click on Close milestone * You get 404 again ### Example Project Here is the setup: https://gitlab.com/groups/milestone-issue/-/milestones Follow the link and click on the test-subgroup-milestone. You get 404. The issue can be reproduced on gitlab.com and we observe it on our on-prem Premium instance v12.8. ### What is the current *bug* behavior? Page not found. ### What is the expected *correct* behavior? Open the subgroup milestone.