My Sunsynk 5kw is doing something similar except the voltage is showing as 540V. No frequency and no Watts. The AC light remains on even though grid has been disconnected and measures 0v at the input. DC side solar is working 100%. Check if you AC light remains on at all times even during loadshedding. My wiring has been checked and all RCD devices are working fine.
The system worked perfectly for two weeks and then this happened.