Currently the default for index.soft_deletes.retention.operations setting is zero. Before we release 6.5.0 we should come up with a reasonable default. Coming up with a good default is tricky, because the index.soft_deletes.retention.operations setting is operation based, but we should settle on a number that allows for soft deleted documents to stay around long enough for CCR while at the same time keeping in mind that keeping soft deleted documents do consume resources.