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this can happen if historicals run out of memory or cpu. I would run queries and monitor historical cpu and memory utilization

check historical logs for any messages, and system logs (for eg OOM-killer)

it was this error - https://stackoverflow.com/questions/16789288/java-lang-outofmemoryerror-unable-to-create-new-native-thread I solved this by update ec2 node ami image which include update ecs agent / docker version