I have a Victron ESS system installed (in a developing country), with 2 MultiPlus-II units (for 240V), a Cerbo, panels, and batteries. Over the past month, I've been seeing some strange behavior and haven't gotten much help from the installer, so I was hoping someone could help point me in the right direction as to what can cause this or what troubleshooting steps we can take.
See the video below for what I see the majority of every day. L1/L2 voltage on the grid ramp up and down (in the range ~114-128) in a constant cycle, along with L1 in AC Loads spiking to 2500W and going back down to 0W in the same cycle. This happens regardless of high or load load in the house. If I disconnect the grid (with a breaker), the problem immediately goes away and everything works as expected. If I reconnect the grid, the problem comes back. If I switch off the entire Victron system (feeding the house with grid power directly), the voltage wobbles maybe 1-2V, but nothing like it does when the system is connected.
What could cause this behavior? I've read about an open neutral somewhere causing similar symptoms, but usually with more extreme voltage variation?