question

@Sufficeguy I suggest checking the inline fuse on the shunt PCB power supply wire... I've seen instances in which one "half-blows", meaning it still passes enough current through to keep the monitor powered, but not enough to let the PCB operate properly... meaning that it sends inaccurate or garbage data to the display head. Given your description of the issue and the particularly odd readings from both the start battery and your house bank, it looks to me like it's most likely a PCB issue, which -while the PCB itself may have gone bad- is very possibly caused by the PCB failing to get a clean voltage from its power supply wire, ie a partially blown or corroded fuse.

Make sure the inline fuse is a 1A quickblow rather than the old 100mA that they used to ship with - it's been determined that the 100mA can tend to drop voltage under load, which can cause garbage readings. Also check the contact points inside the fuse holder itself to be sure they're clean; the slightest buildup of rust or corrosion inside can cause erratic readings.

If the problem persists, I'd contact the Victron distributor from whom you purchased the unit, as it's very possible that the PCB has gone bad and should be replaced under warranty; it's also possible that the display head has gone bad, or rather the data processing of the head. The good news, of course, is that you can leave the shunt itself in place so that your system stays operational.