@Henry I got a response from ZenDure
"We would like to explain that currently our device operates under the logic that if the MQTT connection drops, it will automatically attempt to reconnect 30 times, once per second. If it still fails to reconnect after 30 attempts, it will not try again and you will need to restart the device or re-enable the MQTT function to reconnect. It is likely that the interval between your HA restarts was longer than 30 seconds, so our device stopped attempting to reconnect. Thank you for your patience and understanding."
So if you are lucky it will reconnect in 30 seconds.