@daphwl
This problem will not occur on SIoT1.3, but it will still occur on mosquitto.
I guess the last solution was to prevent mqtt disconnection caused by blocking, but the blocking problem has not been solved.
Maybe somewhere still need to be sloved.
This issue is not fixed for me. I am still experiencing the same issue described by OP after making this change to WifiClient. Please see: mqtt_basic does not work when combined with serial communication in loop() · Issue #245 · ambiot/ambd_arduino · GitHub