Been following this thread with interest because I had almost the exact same issue last summer with my Multiplus II 3000. Took me ages to nail down what was causing it.
In my case it turned out to be the battery voltage dropping just enough during a cloud pass to trigger the low voltage passthrough threshold — even though the SOC looked fine on the Cerbo. The voltage sag was only momentary but the Multiplus was reacting to it faster than the BMS could communicate the actual state to the system.
A couple of things worth checking:
- What are your DC input low/cutoff voltage settings set to in VE.Configure? Mine were left at defaults which were way too conservative for my Fogstar Drift LiFePO4 cells
- Is your battery cabling adequate? Even slightly undersized cable can cause enough voltage drop under load to fool the unit
- Are you on the latest firmware? There were some passthrough-related quirks fixed in more recent Multiplus II firmware
What battery type are you running and how is the system monitoring SOC — is it BMS-controlled or using the Victron shunt? That detail seems to make a big difference in how the Multiplus behaves.
Also curious whether it's happening at a consistent time of day or truly random? Mine was almost always around midday when the inverter load was highest, which was the clue that eventually pointed me toward cable resistance as part of the problem.
Would be good to hear what others have found — this seems to come up fairly regularly and there doesn't seem to be one definitive answer anywhere.
