On mediawiki.org in latest Chrome on Mac. Notifications from other wikis enabled.
Failed to load resource: the server responded with a status of 503 ()
https://www.mediawiki.org/w/api.php?action=query&format=json&meta=notifications¬sections=message¬format=model¬limit=25¬unreadfirst=1¬prop=list%7Ccount&uselang=en¬crosswikisummary=1¬wikis=bjnwiki%7Ctest2wiki%7Cptwiktionary%7Corwikisource%7Ctawiki%7Cilowiki%7Cptwikisource¬filter=!read&_=1463097831813
Dev Tools / Network:
It's a text/html response (the standard one from Varnish).
Request from 2a02:c7d:51f8:1200:e503:d025:38d8:a4af via cp1067 cp1067, Varnish XID 2969230333 Error: 503, Service Unavailable at Fri, 13 May 2016 00:04:44 GMT