3-phase system: L2 and L3 do not invert when grid is connected (only L1)

Q&A and troubleshooting
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Small update regarding our troubleshooting:

We performed a complete physical swap of the L1 and L2 inverters and tested again. The behaviour is still exactly the same, so I can now fully exclude any hardware-related issue with the units themselves**.**

  1. Cerbo GX reset to factory defaults
    We also tried restarting the Cerbo GX and performing a full reset according to the official procedure:
    https://www.victronenergy.com/media/pg/Cerbo_GX/en/reset-to-factory-defaults-and-venus-os-reinstall.html
    This included wiping the configuration and reinitialising the device, but it did not change the behaviour either.

  2. Swapping L1 and L2
    After swapping the units, the system continues to invert only on L1. When the former L2 inverter was placed in the L1 position (master), it behaved exactly like the previous master. Therefore, the inverters are OK and hardware is now fully ruled out.

  3. Testing older assistants from another identical installation
    We even loaded the exact same (older) ESS assistant configuration that we use on another site with identical hardware, where L2 and L3 invert/export normally. Unfortunately, this made no difference — the issue remains unchanged.

  4. Modbus register comparison
    I repeatedly compared all relevant Modbus registers between both installations, and there is no mismatch or invalid value that could explain the behaviour. Everything appears consistent across both systems.

Additional finding – DESS settings cannot be changed

During this process I also discovered another serious issue:
After resetting the Cerbo GX, I was unable to re-enable the DESS system. One record showed a battery capacity of 0 kWh, so I attempted to correct it to 21.6 kWh — but DESS parameters cannot be changed at all.

The system shows the green confirmation message (“Setting accepted”), yet none of the changes are applied.

It appears I am not the only one. Multiple users report that DESS settings simply cannot be modified and always revert back, even though the GX device confirms the request:

At this point we have exhausted almost every technical possibility on the configuration and hardware side.
Since the system behaves exactly the same after all resets, firmware downgrades, inverter swaps and complete reconfiguration, it increasingly looks like there may be some hidden firmware-related issue involved.