Current unbalance in VFD drive by G5 yaskawa.

The reason may be the unbalanced voltage between 3 phase of your supply system.

voltage in supply system is balanced and it is 409v,410v,404v.

is it new motor or rewound motor?.

At low load, the 4-6V of voltage imbalance that you have is enough to produce a small current imbalance. ~1A imbalance is negligible on a approx 20A drive. Don't worry about it unless it reaches 5-10A at full load. If it does, look for the reasons for the line voltage imbalance. The drive is not likely to be the cause for the current imbalance. The line voltage imbalance is more likely it.

u must check the incomming supply voltage

if it is unbalanced

Voltage at source can differ from voltage in motor winding due to resistance in the supply circuit cable terminations. This could cause a difference in current values.

please check the incoming voltage if it is balance, considering that the motor have balance resistance and high insulation in all three (3) phases. If it is found unbalance, expectedly the current will have too.