Random missing page from the cache but present in the database

How to reproduce:

• it is not clear how this happens, the state just occurs from time to time on the wiki
• all the places where it was observed it was on farms with subwikis - but it could also happen in single wiki mode
• it was observed for user pages, group pages, server descriptor pages - this list is not complete.

When it happens, the defect is that there is one page (document) of the wiki that appears to not exist: navigating to the URL of that page / document displays "This page does not exist". No recent action was taken on that document or anything, it looks as it has just "disappeared" .
However, in other places the page is listed as existing: e.g. in livetables or elsewhere.
In the database, the document exists in the xwikidoc table.

Clearing the xwiki cache using the admin tools extension (or restarting the wiki) fixes it, the document is displayed correctly as existing.

Thus, the cause seems to be a wrong information about the existance of the document that is stored in the cache .

A lot of the times, these missing documents have impacts on evaluating rights on various resources, so they will be noticed, functionally, as a rights problem.