I have 4x Victron Multiplus-2 3000/48 stacked for 120/240, then a Fronius 7.6 AC coupled (only 5.4kw PV hooked up to it for now) and it curtails absolutely perfectly! I am completely off-grid. The assistant you use for off-grid with the Victrons is different than the grid-tie assistant. Off-grid just uses frequency shift for curtailing and NOT communication! I do have communication set up for monitoring purposes, but it does not use communication to curtail! I have an electric dryer and have never had any issues with the system when the dryer kicks on and off! (That would be a 6,000w instant swing, BTW.)
Early on I had "tweaked" the frequency shift setpoints in the Victron PV Assistant, and did not realize, but had set the top end too low.
What would happen then was:
-batteries got full> frequency shifted slightly, but not enough> battery voltage climbed on up over a minute or 2 of time> battery BMSs shut down from overvoltage> Victron inverters shut down from battery overvoltage (Extra high spike of ~65-70V was caused from power flow after BMS shutdown!)> AC voltage climbed to ~270V> Fronius shut down from AC overvoltage>batteries and Victrons powered back up
All of this happened quickly enough that I only saw the AC overvoltage shutdown until I began to really watch what was happening. Then it all clicked..... I went back into those assistant settings, set them to factory default, and all my issues went away!
Maybe I like playing with things too much....