No idea, should never happen unless it doesn't find a config. Reason *might* be given in the log when that happens though.
Might be, but I normally try to avoid to add things that merely fix something within the game. As this could be seen as being against the game "rules" I might be looking into adding this to the core game. No promises on either if or when that will happen though.
Depends on the reason. Mod updated for A13? Information in the log?
Old releases can be found in the same folder as the latest archive. Added a section to the wiki page with that info
Planned for a future release, especially when adding the more playerlist centric stuff. For now there is no easy way without changing the JS code.
Is that server modded (items.xml / blocks.xml) by any chance? (I think I know what it is but at least in vanilla servers this shouldn't be possible)
Definitely not with a client update and also for the server only if there are changes to the server code that break compatibility which again should only happen for major releases. Doesn't hurt to update though whenever there is a new release of the mod