I guess theres communication between the BMS and Cerbo? So i guess the battery voltage that is reported in VRM is coming from the BMS directly, at 52.83V. The smartShunt however reports 53.28V. Since theres no current flowing, that voltage difference to me is way too big. I guess you have a bad/loos connection somewhere, some contact resistance or similar issue. If theres no current flowing, then the voltages should be nearly equal. Also double check them with a multimeter