<!--- Please read this! Before opening a new issue, make sure to search for keywords in the issues filtered by the "regression" or "bug" label: - https://gitlab.com/gitlab-org/gitlab/issues?label_name%5B%5D=regression - https://gitlab.com/gitlab-org/gitlab/issues?label_name%5B%5D=bug and verify the issue you're about to submit isn't a duplicate. ---> ### Summary "404 Page not found" when clicking on a subgroup's milestone in the parent group milestones view. ### Steps to reproduce 1. Create a Top-level group 2. Create a subgroup 3. Create a milestone for the subgroup 4. Navigate to the top-level group milestones screen 5. Click on the milestone from the subgroup 6. Instead of the milestone, you get 404 Not Found page. ### Example Project Tested Project : https://gitlab.com/groups/test_group19/-/milestones The issue can be reproduced on gitlab.com and we observe it on our on-prem docker instance **[+v12.9 (and 12.8.x)+]** ### What is the current *bug* behavior? Page not found ### What is the expected *correct* behavior? Open the subgroup milestone ### Relevant logs and/or screenshots  ### screenshots