On commons, I'm getting default sidebar, instead of customized version from [[commons:MediaWiki:Sidebar]]. My user language is english. This happens to me both when logged in and logged out.
(If this happens on non-en wikis, it would probably be pretty serious).
Relevant thread: https://commons.wikimedia.org/wiki/Commons:Village_pump#Where.27s_the_upload_button.3F
Version: unspecified
Severity: major