"8" display in offline auto tuning means forced stop by the operator.
This means that you stopped operation before tuning completes. 　
With this forced stop, the tuning data is not stored in the inverter and the previous data is used when you start the motor.
It is considered this caused the overload at low speed. 　
Since the inverter capacity is one-rank higher than the motor capacity, tuning is not necessary and you can drive the motor under normal V/F control.
Since the motor is the constant-torque motor, adjust the Pr.0 (Torque boost) setting value. (The initial setting is 6%. Reduce it so that the current does not increase.)