Logs would look like: INFO 2021-06-09 19:14:56,039 [[MuleRuntime].uber.06: [validationtest].batch-job-validationtestBatch_Job-work-manager @6de10f3e] [processor: validationtestFlow/processors/1/route/0/route/0/aggregator/processors/0; event: bfb751e1-9939-11eb-9f69-02053763653a] org.mule.runtime.core.internal.processor.LoggerMessageProcessor: [ "\"A\"", "\"C\"", "\"D\"" ] -- INFO 2021-06-09 19:15:02,486 [[MuleRuntime].uber.06: [validationtest].batch-job-validationtestBatch_Job-work-manager @6de10f3e] [processor: validationtestFlow/processors/1/route/0/route/0/aggregator/processors/0; event: bfb751e1-9939-11eb-9f69-02053763653a] org.mule.runtime.core.internal.processor.LoggerMessageProcessor: [ "\"E\"" ] Batch aggregator value is 3. Hence in first time it will print ["A", "C", "D"] and in next iteration it will print [ "E" ] -------------------------------------------------------------------------------------------------------------------------------------------------- Correct answer is [ "E" ]