Side-by-side diff does not show proper highlighting (BB-14424)

When I pull up a pull request page on my browser, I get a list of the files that have changed.
For each file, I get the diffs in a single view with the changes marked by grey, red (deletions) or green (additions) highlighting.
However when I click on the button for the "Side-by-side diff" the colored highlighting is now broken. It shows grey without the red/green in some of the places, where it used to show the changes. This makes it harder to read the differences.
I think it may happen in sections of code that have both deletions and additions because the sections that are only additions still show green and the sections that are only deletions show red. If a section of code has additions and deletions on the same line it just shows all grey and you can no longer see the characters that have changed