Github user tabish121 commented on the issue:
https://github.com/apache/activemq-artemis/pull/1695
@michaelandrepearce it depends on what other URI options you've set on the
5.x client, it will at times switch back to sync based on other configuration.
For alternate reference the Qpid JMS AMQP 1.0 client will also send
non-persistent messages async by default, errors would be reported to the
connection exception listener for JMS 1.1 sends and to the CompletionListener
for JMS 2.0 async sends as one would expect.
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