Just to point out that the syndrome of the missing postbox (JS3 or JS4) can be caused by a translation string containing an error or a line break. Double check your language file xx-XX.com_community.ini.
In my case, the string COM_COMMUNITY_EVENTS_LOCATION_DESCRIPTION was in cause, with a line break causing a javascript error (see console)… and no more postbox (Stream, events stream…). Removing one linebreak and the postbox was there again.