It is possible for the oplogTruncateAfterPoint logic to fail to find a oplog entry w/ timestamp LTE WT's all_durable timestamp if the oplog truncation logic manages to delete older oplog entries very quickly. There is nothing stopping this behavior because there currently are no special rules to avoid truncating the oplog needed by the oplogTruncateAfterPoint logic in WiredTigerKVEngine::getPinnedOplog().