so when we do a search in ES we do it in 2 roundtrips. To make sure it's consistent we register a search context on every shard during the first roundtrip. The second roundtrip passes the context ID on to make sure we operate on the same point in time snapshot as the first roundtrip. Now if something closes the search context ie. if it times out (5min by default) you will see this message. It's possible for instance in situations like scan/scroll that if the users is not coming back we might clean up the context in that case. Do you use scan/scroll?