Steps to replicate the issue (include links if applicable):

• Go to some Wikidata item
• Click a sitelink in the multilingual category
• Try to go from that page to a sister project

What happens?:

Depending on the site, the sitelinks do not appear, or appear only when logged out.
For example, https://www.wikidata.org/wiki/Q121 links to https://abstract.wikipedia.org/wiki/Q121, https://www.wikifunctions.org/wiki/Z16107, and https://commons.wikimedia.org/wiki/July, but only the latter links to sister sites in the tools menu, and only when logged out. On Wikispecies they're also shown only when logged out. I double-checked and it's not my UserCSS. There are no errors in the browser console.
edit: Also not appearing on Meta and Wikidata itself, confirmed with https://www.wikidata.org/wiki/Q28054658.
Another example to help with bisect: archived working 2026-03-12, broken now even when logged out (the sitelink is still set).

What should have happened instead?:

Sitelinks are shown under tools menu

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):
Live wikis

Other information (browser name/version, screenshots, etc.):
FF 152

I don't think this is related to T425249 because I recall the sitelinks working after 2026-05-03 when that was filed.