I got this report of a category that couldn't be adapted, which translating from English to Hebrew:

The category Ellsworth Mountains was linked to Hebrew in September, but apparently it couldn't be adapted.

I couldn't reproduce it myself, but the screenshot shows that it happens in at least some cases.

My suspicion is that even though a sitelink exists, the Wikidata cache wasn't purged, so the API request that checks for the availability of the category couldn't find a corresponding category. Perhaps we can purge it before querying it.