If a message has a lock symbol then it is locked by a consumer. Keep in mind that a consumer has a cache of 500 messages by default. Up to this size is prefetched and delivered to the consumer, if possible. These messages aren't consumed yet (they are only in the consumer's cache) so the messages are locked. The consumer cache size is determined by the attribute "smqp-consumer-cache-size" of the connection factory the consumer did use.