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This is a WARN and not ERROR, but I understand that can be irritating. I've seen people improve this by using http-based segment management, easing up the pressure on zookeeper. To do this, you'd change overlord properties to set druid.indexer.runner.type to httpRemote, and coordinator settings to set druid.coordinator.loadqueuepeon.type to http. You could try that (you'd have to restart overlord and coordinator, of course).