Paul, check if the issue you are facing is same as described in this article Article Viewer | PTC:
The AutoMapping functionality of the MQTT and MQTTSubscriber Thing Templates automatically establishes a subscription and a publish arrangement with the MQTT broker for all properties defined on the Thing.
- MQTT messages sent to the broker with topics corresponding to an auto-mapped property are automatically subscribed and will update the property values on the Thing when received.
- Property value changes on the Thing will be sent out as Publish messages to the MQTT broker, which then are sent back to ThingWorx as a subscribed topic update.
- A ThingWorx subscription that is configured to change a property value on an MQTT Thing in response to a data change on that same MQTT Thing can result in a blocked thread.
Article provides also possible workaround:
Define publish / subscribe subscriptions for properties manually on the Thing in question.
- For properties that must be updating from MQTT, make sure to set the subscribe flag on the mapping that is created.
- For properties that should not be sending out updates to MQTT, do not set the publish flag on the mapping.
- Avoid setting up mappings that do both publish and subscribe, especially where the property is likely to be modified during an MQTT triggered event.