This is an update to the other topics I created about this issue (RegExp interrupted and Interrupted waiting for mutex)
In my environment I am using Kafka, and it is pulling from a firehose of data and pushing to a sorely overloaded ES server (and constantly falling behind). I recently upgraded to LogStash 5.6.2, and that version passes Kafka feedback to the console. As a result of that feedback (it was complaining about threads being too slow to service the Kafka event queue), I shrunk the Kafka batch size waaaaay down (it's unset by default -- according to the documentation), and now I no longer get these errors and LogStash isn't crashing anymore.
So, FYI in case anyone else is experiencing these errors/crashes with LogStash.