Find pages that have an interwiki link to a nonexistent page. Correct the error. If the change is more than just capitalization, an iwlinks query picks up the change immediately. If the change is only to the capitalization, it isn't picked up. Based on a sample of 4 links from en wikipedia to en wikisource.

Repro:
https://en.wikipedia.org/w/api.php?action=query&prop=iwlinks&titles=Caraway
Should list prefix: "s", *: "1911_Encyclop\u00e6dia_Britannica/Caraway" but doesn't.
This iwlink was corrected from the nonexistent "caraway" on 28 April (the page has been edited once since).

Other similar enwiki pages: "1517 in art" (fixed a fully-capitalized word to the correct initial-cap on 8 April), "Archosargus probatocephalus", "Pediment". Each of these is the current version.

I've found other inconsistencies around whether the query actually lists a nonexistent page in the "other" wiki, but need to do some more to figure out an accurate repro (will try to find out connections between does or doesn't). If I find that I'll report and link this report (unless I've waded into a known bug).