Lynx Shunt throwing Low Voltage alarms consistently - can’t find low voltage

DIY
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I’m helping a fellow boater with their boat. He has two lynx distributors connected to a lynx shunt. Bottom side for input of 4 314AH WattCycles in parallel, top side for output to MPPT, DC-DC. He had the DC-DC hooked up backwards, which we fixed, the starter bank was under 12 V. I expected the error to go away. Yet, many times after, once applying power, the voltage stayed clear at 13.13v with a Low voltage set off of 12v, and on our multimeter we would never see the voltage drop on either input or output side prior to the system suddenly sending off a low voltage reading of 8.4V. I noticed he did not have a common ground setup on his vessel. 12v, wasn’t grounded to the motors. Could that be the issue or could there be something else? Other theory is the Lynx Shunt is faulty, as all other devices were disconnected.