ActiveMQ Artemis scheduled messages get stuck - jms

Question

I have messages not getting delivered, where I would hope for somebody being able to provide some insights.
Only at times I end up in the following state on my broker - observed via the management console on some specific queue:
countMessages() -> 17
browse() -> empty list
listScheduledMessages() -> shows 17 messages
retryMessage("with some message id") -> the amount of scheduled is then reduced to 16
My application does not send any scheduled messages.
The JMSXDeliveryCount of those scheduled messages is always 0 - so it seems they are not in the process of being redelivered due to some exception in the consumer.
broker.xml:
<configuration xmlns="urn:activemq" xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:activemq /schema/artemis-configuration.xsd">
<core xmlns="urn:activemq:core" xsi:schemaLocation="urn:activemq:core ">
<name>xxx-artemis-activemq-artemis-master-0</name>
<persistence-enabled>true</persistence-enabled>
<journal-type>ASYNCIO</journal-type>
<paging-directory>data/paging</paging-directory>
<bindings-directory>data/bindings</bindings-directory>
<journal-directory>data/journal</journal-directory>
<large-messages-directory>data/large-messages</large-messages-directory>
<journal-datasync>true</journal-datasync>
<journal-min-files>2</journal-min-files>
<journal-pool-files>10</journal-pool-files>
<journal-device-block-size>4096</journal-device-block-size>
<journal-file-size>10M</journal-file-size>
<journal-buffer-timeout>12000</journal-buffer-timeout>
<journal-max-io>4096</journal-max-io>
<disk-scan-period>5000</disk-scan-period>
<max-disk-usage>90</max-disk-usage>
<acceptors>
<acceptor name="artemis">tcp://0.0.0.0:61616?tcpSendBufferSize=1048576;tcpReceiveBufferSize=1048576;protocols=CORE,AMQP,STOMP,HORNETQ,MQTT,OPENWIRE;useEpoll=true;amqpCredits=1000;amqpLowCredits=300;amqpDuplicateDetection=true</acceptor>
<acceptor name="amqp">tcp://0.0.0.0:5672?tcpSendBufferSize=1048576;tcpReceiveBufferSize=1048576;protocols=AMQP;useEpoll=true;amqpCredits=1000;amqpLowCredits=300;amqpDuplicateDetection=true</acceptor>
<acceptor name="stomp">tcp://0.0.0.0:61613?tcpSendBufferSize=1048576;tcpReceiveBufferSize=1048576;protocols=STOMP;useEpoll=true</acceptor>
<acceptor name="hornetq">tcp://0.0.0.0:5445?anycastPrefix=jms.queue.;multicastPrefix=jms.topic.;protocols=HORNETQ,STOMP;useEpoll=true</acceptor>
<acceptor name="mqtt">tcp://0.0.0.0:1883?tcpSendBufferSize=1048576;tcpReceiveBufferSize=1048576;protocols=MQTT;useEpoll=true</acceptor>
</acceptors><security-settings>
<security-setting match="#">
<permission type="createNonDurableQueue" roles="amq"/>
<permission type="deleteNonDurableQueue" roles="amq"/>
<permission type="createDurableQueue" roles="amq"/>
<permission type="deleteDurableQueue" roles="amq"/>
<permission type="createAddress" roles="amq"/>
<permission type="deleteAddress" roles="amq"/>
<permission type="consume" roles="amq"/>
<permission type="browse" roles="amq"/>
<permission type="send" roles="amq"/>
<permission type="manage" roles="amq"/>
</security-setting>
</security-settings>
<cluster-user>exampleUser</cluster-user>
<cluster-password>secret</cluster-password>
<address-settings>
<address-setting match="activemq.management#">
<dead-letter-address>DLQ</dead-letter-address>
<expiry-address>ExpiryQueue</expiry-address>
<redelivery-delay>0</redelivery-delay>
<max-size-bytes>-1</max-size-bytes>
<message-counter-history-day-limit>10</message-counter-history-day-limit>
<address-full-policy>PAGE</address-full-policy>
<auto-create-queues>true</auto-create-queues>
<auto-create-addresses>true</auto-create-addresses>
<auto-create-jms-queues>true</auto-create-jms-queues>
<auto-create-jms-topics>true</auto-create-jms-topics>
</address-setting>
<address-setting match="#">
<dead-letter-address>DLQ</dead-letter-address>
<expiry-address>ExpiryQueue</expiry-address>
<redelivery-delay>1000</redelivery-delay>
<redelivery-delay-multiplier>5</redelivery-delay-multiplier>
<max-redelivery-delay>360000001</max-redelivery-delay>
<redelivery-collision-avoidance-factor>0.15</redelivery-collision-avoidance-factor>
<max-size-bytes>-1</max-size-bytes>
<message-counter-history-day-limit>10</message-counter-history-day-limit>
<address-full-policy>PAGE</address-full-policy>
<auto-create-queues>true</auto-create-queues>
<auto-create-addresses>true</auto-create-addresses>
<auto-create-jms-queues>true</auto-create-jms-queues>
<auto-create-jms-topics>true</auto-create-jms-topics>
</address-setting>
</address-settings><addresses>
<address name="DLQ">
<anycast>
<queue name="DLQ"/>
</anycast>
</address>
<address name="ExpiryQueue">
<anycast>
<queue name="ExpiryQueue"/>
</anycast>
</address>
</addresses><connectors>
<connector name="xxx-artemis-activemq-artemis-master-0">tcp://xxx-artemis-activemq-artemis-master-0.xxx-artemis-activemq-artemis-master.artemis.svc.cluster.local:61616</connector>
<connector name="xxx-artemis-activemq-artemis-slave-0">tcp://xxx-artemis-activemq-artemis-slave-0.xxx-artemis-activemq-artemis-slave.artemis.svc.cluster.local:61616</connector>
</connectors><cluster-connections>
<cluster-connection name="xxx-artemis-activemq-artemis">
<address/>
<connector-ref>xxx-artemis-activemq-artemis-master-0</connector-ref>
<retry-interval>500</retry-interval>
<retry-interval-multiplier>1.1</retry-interval-multiplier>
<max-retry-interval>5000</max-retry-interval>
<initial-connect-attempts>-1</initial-connect-attempts>
<reconnect-attempts>-1</reconnect-attempts>
<message-load-balancing>ON_DEMAND</message-load-balancing>
<max-hops>1</max-hops>
<static-connectors>
<connector-ref>xxx-artemis-activemq-artemis-master-0</connector-ref>
<connector-ref>xxx-artemis-activemq-artemis-slave-0</connector-ref>
</static-connectors>
</cluster-connection>
</cluster-connections><ha-policy>
<replication>
<master>
<group-name>xxx-artemis-activemq-artemis-0</group-name>
<check-for-live-server>false</check-for-live-server>
</master>
</replication>
</ha-policy>
</core><core xmlns="urn:activemq:core">
<jmx-management-enabled>true</jmx-management-enabled>
</core>
</configuration>
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