Packets whose index is 0 are considered as malformed packets by the MQTT broker. If such thing happens, the client is disconnected by the broker. The value of the packet_id_counter variable is now calculated in a way that it is always different from 0 to avoid unwanted disconnections.
@brentru : this is a pull request to address this issue: https://github.com/adafruit/Adafruit_MQTT_Library/issues/203
Packets whose index is 0 are considered as malformed packets by the MQTT broker. If such thing happens, the client is disconnected by the broker. The value of the packet_id_counter variable is now calculated in a way that it is always different from 0 to avoid unwanted disconnections.