The issue was not related to the size of the queue, but instead to the fact that when to destination that we are sending those logs to had connectivity issues (which was causing quite a lot of timeout errors), NiFi was using a lot of a significant number of threads to retry sending the logs to the InvokeHTTP destination. This high usage of threads was causing ListenSyslog to not function properly - it was dropping the logs that it was supposed to receive. ... View more