Merge request comment diffs are missing the highlighted line

Summary

We've recently (4 months ago) become GitLab Enterprise Edition (10.5.4-ee) users, moving from Gerrit to GitLab.

This bug is making it hard to see exactly which lines of code comments relate to.

Steps to reproduce

  1. Open a merge request
  2. Add a comment on a single line
  3. The diff shows multiple lines

Which line has been commented on??

From experience, we now know it's the last line. But new users are struggling with this!

What is the current bug behavior?

Diffs for review comments on specific lines don't show the line highlighted.

Merge request view
Without highlighted line 👎

Merge_Request_view

Diff view
With highlighted line 👍

Diff_view

What is the expected correct behavior?

I'd expect the Merge Request comment diff to show the highlighted line the comment belongs to, just like diff view.