The core client will truncate messages if a client consumes messages and saves the Message objects in a collection for later processing. This happens here:

https://github.com/apache/activemq-artemis/blob/eb7b0b09467c0395dbb5d628ccb93734feae1f5e/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/client/impl/ClientConsumerImpl.java#L209

It would be nice if the client would log a warning when data is left over and is being truncated.