We have a NEXT STEP-2 reg ...there is a file in the Files section showing how I did it
The reg in the Leece Neville alt is not designed to charge deep cycle batteries.
Keeping the voltage always at 28.8V will eventually kill your AGM batteries. They need a bulk, absorption, float regimen if they are to be cared for properly.
600W solar panels and a Victron MPPT controller
Leece Neville 175A engine alt with Next Step-2 reg
Victron Skyalla 100A charger
Promariner 30A charger
and they are all set to the same absorption and float voltages.
Diodes fail open, I don't think that can be the cause of your problem.
Somewhere on some device that has both 24VDC feed AND a connection to the bonding system, there is a connection between -ve and the bonding connection...and it may not be a metal to metal contact , frequently it is through the sea water.
Elyse SM437 Yasawa-i-rara