Hey guys, I know there have been a bunch of questions lately about indexes getting stuck in the `installed` state, and I recently discovered some more interesting potential causes for the problem; please see #5 in my StackOverflow answer here: https://stackoverflow.com/questions/40585417/titan-db-ignoring-index/40591478#40591478
TLDR; you might have phantom JanusGraph nodes that are unable to acknowledge index existence, and thus the index will never move to `REGISTERED`. You may also have issues with backfilling of the queue, but I would definitely expect the former first.
