Until about a few weeks ago, the "Other sites" section of an item let me add sitelinks to Commons or Wikidata. Now, it still displays existing Wikidata sitelinks in that section, but I can't seem to add any new ones there.
For example, https://www.wikidata.org/wiki/Category:User_li-1 is currently linked to https://www.wikidata.org/wiki/Q6333331 but https://www.wikidata.org/wiki/Category:User_li-0 is not linked to https://www.wikidata.org/wiki/Q9433115. If I click "edit" in the "Other sites" header for Q9433115 and start to type "wikidata", no site appears.