Flickering note when changing tabs

Summary

Note (comment) flickers when it was loaded with AJAX and we changed tabs.

Steps to reproduce

1. Create an issue
2. Assign it to yourself
3. Switch to a different tab
4. Go back to the tab with the issue - system note about the assignment should appear
5. Switch to a different tab
6. Go back to the tab with the issue and observe the note - it flickers

This happens on dev.gitlab.com, but not on gitlab.com right now.

/cc @MadLittleMods