We had a misbehaving application using a database named "adaptive_recall_production". According to the log it was doing everything in triplicate (maybe some confusion with configuration, we do have 3 instances in this replica set). It was also trying to automatically create indexes for it's collections, but didn't think the index it created was the correct one, so it would drop it and recreate. Somewhere along this path the server segfaulted.

Log attached.