It looks like the genres are no longer making it into the release dumps. I’m using the json dumps at http://ftp.musicbrainz.org/pub/musicbrainz/data/json-dumps/ and some automated tests recently started failing because of the missing data. When I grep the untarred release.tar.xz file, it shows this for every release:
So the key and array seem to be included, just not the genre values. Naturally, not all releases have genres defined, but the dump doesn’t currently include genres for any releases. I’m not sure exactly when it changed, but it was within the last week or two.
Many thanks for all your efforts,