I had a similar problem and only got it properly sorted when I finally got a smart meter. I also have a long extension on the ct coil which was giving wildly inaccurate grid readings causing the inverter to send lots of power to the grid. In the end setting the ct ratio to 2300 and grid trickle to 500 actually results in about a 20w trickle average and much more effort use of solar and battery. I just live with the useless grid usage numbers on the inverter. I assume it's down to interference on the long cable.