Yellow highlighting fails in Who Wrote That, even when a given run is otherwise working. I.e., after WWT load completes and clicking page text successfully shows the pop-up dialog box with who/when and the underlying diff link, which when clicked goes to the correct diff page, but all without any yellow highlighting.
This happens intermittently. The last few days have been clear, but today I had two unhighlighted pages in a row, right after having viewed the same page ([[ https://en.wikipedia.org/wiki/Transgender#Terminology | Transgender ]]) with highlighting a few minutes earlier. I'm sorry I don't have any reproduction steps for you, but it's occurring too intermittently to reproduce, or to remember exactly how I got there, other than clicking the WWT link I have in the sidebar at en-wiki after having installed the extension.
Spawned from comment T318746#8285520 as suggested by @TheresNoTime.
Possibly of interest to @MusikAnimal, @Sennecaster, @Danbloch, @Tamzin.