The special page unconnected pages shows sign of slowly accumulating false positives, pages that is listed as "unconnected" even if they are connected. Doing a purge removes the pages from the list, so it seems like it could be a lost update of some sort.
People at the community at nowiki complains from time to time that they must do an explicit purge before the page is updated after changes on Wikidata. Whether this is due to long delay before the automatic update, or the automatic update is lost, I don't know. I suspect it is a bit of both.
I purge the pages on "unconnected pages" once in a year or so to get rid of false positives. It is not a very pressing issue, but it is annoying.