After the batteries are matched, why are the charging rates somewhat higher and some lower?

It may be related to the capacity or internal resistance of the battery. You can first lower the high or low battery separately or charge it up to the same voltage as other batteries. Charge and discharge several times to see if the voltage of the string of batteries is still high during charging, it means the capacity of the string of batteries is low. Otherwise, the battery capacity is high. It is also related to the assembly method. Try to make the series wires and parallel wires the same thickness and length, or check the welding point of the balance wire, it may also be affected. Note that the protection board only detects the voltage of the battery and does not change the voltage of the battery