mqtt client id should be unique under your amazon IoT account
#define AWS_IOT_MQTT_CLIENT_ID "MyDock123 - updater" ///< MQTT client ID should be unique for every device
but Amazon document didn’t mention what will happen if not unique
here is my test:
the previous connected one will be kicked offline when next one connect
WARN: disconnectCallbackHandler L#70 MQTT Disconnect Auto Reconnect is enabled, Reconnecting attempt will start now ERROR: main L#264 An error occurred in the loop :-12.
For Mass Production
using mac address as unique ID maybe a good idea