Unused menu entries
Three of the six main menu entries on the left menu are not in use at the moment. Currently Community portal leads to a pretty meaningless page, while Current events is a deleted page, and Help is a non-existant page. I suggest you either find better pages to link to, fix the pages in question, or cull them.
Unless there is a specific help page, I suggest you replace the help entry with a link to either support or FAQ, latter probably better. A community portal could be useful, do we have something similar? We have current events, but not many enough to deserve it's own page. Perhaps link to Project:News instead?
You probably are seeing a bug in MediaWiki where the sidebar occasionally reverts to default settings.
Could be. It is not occasional for me though, it is consistent when I use 'en' as interface language.
Has the bug been reported?