Hi William,
I too recently had a Growatt 500es installed in Sri Lanka, and had it mysteriously get fried just as you said - 3 am, load of around 600w. Have had a replacement, but no answer as to why this happened. I've also just noticed this morning (around 2am) that my new inverter showed a freak spike of around 1600w. Stranger still, there is no corresponding draw from the grid or the battery.
Have you experienced anything similar?