More info, where is the SOC coming from, what make of battery.
If it is a 3rd party battery with comms to the GX device, some have poor SOC calculation and the BMS ignores small currents so the battery could fully discharge without the SOC falling.
If it is a Victron Shunt or BMV battery monitor or Lynx BMS then the settings could be wrong or the wiring wrong, see the FAQs below.