Can't expand the amount of context around a diff'ed area when the file is over 10,000 lines. (BB-12744)

On the pull request overview tab, diffs are shown for each file chunk that has changed. If the file happens to be over 10,000 lines, the small ellipsis button that shows more context around the diff'ed area, does not work. I see the pinwheel pop up next to the ellipsis, denoting an asynchronous request has been sent, but nothing else happens.

To be clear, it is not when the diff'ed section is over 10,000 lines. It happens when the file being diff'ed is over 10,000.