I have the same issue. We turn on AC Input ignore a few times a day. Every time AC input ignore fires we get a grid loss notification even though the grid is still present.
Workaround was to disable grid loss monitoring on Venus/Cerbo. Then create a custom flow in node-RED that activates the grid loss. This generates a message in VRM as well.
I use ignore AC and can still see AC voltage and I don’t have such a problem with an alarm set up in VRM? I’m not using Node Red or anything else for this.
My quattro is on 510 and my Cerbo on 3.66. I’m not using ESS but I don’t know if that is significant. Everything works flawlessly. When my grid voltage limits set up under VRM are hit, I get an alarm as set up, including on both my phones, with a reading of the present voltage