Some of my mediawiki instances broke when editing a page with VisualEditor on REL_30 today bringing HTTP 416 Errors related to Parsoid.
Strangely this error only occured when editing existing pages, simplyfied as curl below:
curl "http://NAME_OF_WIKI_HERE/api.php?action=visualeditor&format=json&paction=parse&page=Main_Page&uselang=en"