I would assume that since the error references current sharing the issue is primarily with how mismatched the total wattage hooked to each inverter is. Im not sure which current the current sharing cables are sharing but i strongly suspect if you distributed the solar wattage more evenly this issue would disappear.
The adding capacitance at PV circuit of each inverter idea.. suggests that you might be trying to clamp/attenuate voltage spikes from the mppt PWM’ing the solar circuit. As far as i know an mppt is like a switching power supply and the circuit will have some.. uhh i forget which term, relating to storing electromagnetic energy which will get dumped back into the circuit when the switching devices open the circuit, making some spiky stuff. The less power youre using the shorter the pulses probably are, which means less drop from VOC, which means voltage spiking from a higher starting point. And a super short pulse would give back a small enough total energy in that spike that a small capacitor could seriously drop the peak voltage of it.. boy is that theory a REACH for someone of my electrical knowledge level. ? Id be curious to know more about that current sharing circuit works and how this capacitance is intended to work.