I was translating the article "Hugo de Jonge" from Dutch to English using the Content translation tool. After painfully rearranging the references (this is unfortunately a Hard Thing), they suddenly disappeared after clicking 'publish'. Not a trace can be found in the wikitext that was published. In the translation tool they were still visible.
Enwiki (first version): https://en.wikipedia.org/w/index.php?title=Hugo_de_Jonge&oldid=809114312
nlwiki: https://nl.wikipedia.org/w/index.php?title=Hugo_de_Jonge&oldid=50285013