Steps to reproduce:
* Go to Special:Watchlist in the mobile view (e.g. https://fa.m.wikipedia.org/wiki/Special:Watchlist?uselang=en)
* Click on the "diff" link for one of the changes
* It will take you to a URL similar to this one: https://fa.m.wikipedia.org/w/index.php?title=Special:MobileDiff/30145260&curid=5381367&uselang=en (note that both a `curid` and an `oldid` are present)
* What you see will ***not*** be a Diff page. It will be the "View" version of the page.
* Compare with https://fa.m.wikipedia.org/w/index.php?title=Special:MobileDiff/30145260&uselang=en with does not have a `curid` and what you get is an actual diff page.
Note that fawiki does not use the same "Watchlist" view in the mobile frontend as most other projects. We are part of some of the design programs (I bet @Ladsgroup can clarify which ones). Don't be surprised if https://fa.m.wikipedia.org/wiki/Special:Watchlist?uselang=en does not look like https://en.m.wikipedia.org/wiki/Special:Watchlist?uselang=en to you.
Of note, the issue with curid confusing what should be rendered is coming up twice now (previously in T260713 where I assumed it was intended behavior, so I revised #CheckUser code to simply not return `curid` when not applicable). Could we have possibly messed up the order in which parameters are consumed such that `curid` is now being checked before others? The issue reported here, with diff links, is certainly new.