In Picard debug log:

E: 22:44:13 Network request error for https://musicbrainz.org:443/ws/2/release/81209d47-16cc-4e81-96bb-54e66925255a?inc=release-groups+media+recordings+artist-credits+artists+aliases+labels+isrcs+collections+artist-rels+release-rels+url-rels+recording-rels+work-rels+recording-level-rels+work-level-rels+tags: Error downloading https://musicbrainz.org:443/ws/2/release/81209d47-16cc-4e81-96bb-54e66925255a?inc=release-groups+media+recordings+artist-credits+artists+aliases+labels+isrcs+collections+artist-rels+release-rels+url-rels+recording-rels+work-rels+recording-level-rels+work-level-rels+tags - server replied: Service Unavailable (QT code 301, HTTP code 200)

On ernie nginx log:

1460407452.771 90.125.158.144 "GET /ws/2/release/81209d47-16cc-4e81-96bb-54e66925255a?inc=release-groups+media+recordings+artist-credits+artists+aliases+labels+isrcs+collections+artist-rels+release-rels+url-rels+recording-rels+work-rels+recording-level-rels+work-level-rels+tags HTTP/1.1" 503 535 z=- up=10.1.1.29:80 ms=0.032 ums=0.032 ol=- h=musicbrainz.org:443

So the server is returning a 503 but Picard logs a 200 ... something very wrong here.