I did look into installing line filters, but the electricians highly recommended against it, plus the extra cost. When they saw the EXTREME voltage and frequency fluctuations, they firmly suggested getting the Growatt out of the equation. The electricians literally laughed saying they never saw anything like it. I have repeated this over and over, but I temporarily replaced the Growatt with a small 2200W Giandel inverter and all of the issues disappeared. I finally installed a Victron Energy Quattro, and again, very clean stable power. The Growatt was the problem.
I run two full size fridges, chest freezer, wash machine and much more all at once and no issues. The Growatt just couldn't handle two fridges running at the same time. And I will repeat this as well. I really wish it would have worked. The Growatt is such a great product that simplifies a solar installation, needing very little space and yet packed full of features. I hope that the future brings changes that will resolve this issue. There are many reports of the exact same issues I had. All of those issues disappeared with other inverters.