`queue.checkpoint.interval` has never been implemented An old [PR](https://github.com/elastic/logstash/pull/6408) has removed it. However, it still references in [here](https://github.com/elastic/logstash/blob/main/logstash-core/src/main/java/org/logstash/ackedqueue/QueueFactoryExt.java#L91), but is skipped in [initialisation](https://github.com/elastic/logstash/blob/main/logstash-core/src/main/java/org/logstash/ackedqueue/ext/JRubyWrappedAckedQueueExt.java#L58-L59)