The repaired kWh meter works well, capacitor and 470 R resistor had blown up.
These Sangamo meters are actually very reliable. This one was connected up into a 12V to 240 volts inverter circuit.
The so called 'pure sinewave' must still have some harmonics on it which destroyed the capacitor in the meter.
As the reactance of a capacitor depends upon the frequency any harmonics may cause extra heating and stress out the dielectric.