What version are you running?
What is the expected output? What do you see instead?
Sometimes the diff display is cut off on the right, making it impossible to read. I suspect it might have something to do with trailing whitespaces (although this happens regardless of whether you enable showing them or not).
This is a problem when using Firefox. On Chrome it is displayed fine.
What operating system are you using? What browser?
Firefox Quantum 58.0.2 (64-bit)
Google Chrome 64.0.3282.167 (Official Build) (64-bit)
Screenshots of Firefox and Chrome view are attached.