This is because the multiplus is being used Only to charge and thus CANT SEE the drain that occurring on that gen battery. The multi pkus only can see what it uses itself and what it charges. To get a proper soc on the gen battery you need a victron smartshunt or bmv installed on the gen circuit.
Also the extra muktiplys should not be connected to the cerbo gx. It may confuse it wuthvthec3 phase stsrem
The correct SOC will be the one coming from the Smartshunt. If you had managed batteries (doesn't appear so) then the one from there would be the choice. In either case you should disable the SOC from all the Multipluses so they can't be seen.
This is a Victron recommendation to all their installers. Multiple sources of SOC is confusing to customers - as you have experienced.
That doesn't necessarily mean that your Shunt is correct. It will need tuning for your installation.
Where turn off that in cerbo gx or other place ?
In the Multis. I use VE.Configure.. https://www.victronenergy.com/live/vrm_portal:remote-veconfigure
