Our battery has a excessive cranking protection feature and very low voltage protection.  Excessive cranking protection logic monitors temperature to limit engine cranking to 10 -30 seconds in any 60 second period, and if exceeded the battery will disconnect from the load to protect the cells and BMS from damage.  Another possiblity is that the voltage dropped too low (<5 volt) during a cold start.  If the BMS disconnects, it will automatically reconnect after a cooldown period (typically 1-3 minutes).