AMQ modules have changed, customers need to update their configuration if they have deployment-structure.xml depending on the module org.apache.activemq.artemis, or have the module defined as a global module.
When moving from EAP 8.0.x to 8.1.y if your deployments are depending on org.apache.activemq.artemis it will fait beccause the module is marked as private. You should change your dependencies so that you use the module org.apache.activemq.artemis.client.