### Summary I'm trying to add comments on my own MR on one the diffs, but when I click **Comment**, the comment is not added. No emails are sent out and nothing appears in the **Discussion** section either. The diff in question has a lot of changes - so much so that it says "Cannot display changes" unless I enable "Hide whitespace". If that makes any difference, I'm commenting on the changed lines. Commenting on other, smaller, diffs in the same MR works. ### Steps to reproduce 1. Submit MR with a large diff containing many whitespace changes. 2. Make sure diff cannot be displayed with whitespace shown. 3. Hide whitespace. 4. Make sure diff is now displayed. 5. Type in a comment on one of the changed lines. 6. Click "Comment". Adding a comment on an unchanged line of a diff often causes the same behavior (doesn't matter if the diff is big or small). I have Firefox 55.0.2 64-bit, Ubuntu 16.04. ### What is the current *bug* behavior? Comment is not added after "Comment" is clicked. ### What is the expected *correct* behavior? Comment is successfully added. ### Relevant logs and/or screenshots None ### Output of checks This bug happens on GitLab.com.