For more information on topic filters, see Topic filters.. Check for topic name errors. MQTT topic names and topic filters are case sensitive. If, for example, your device is publishing messages to Topic_1 (with a capital T) instead of topic_1, the topic to which you subscribed, its messages would not appear in the MQTT client.
https://docs.aws.amazon.com/iot/latest/developerguide/view-mqtt-messages.html

