I guess it's the num_histoty_steps that is creating problem in convergence, I reduced the k-point to na=13, nb=7, and nc=141 and num_history_steps=12. The zero bias calculation converged in 147 steps, but 0.05V, 0.3V, 0.35V, 0.4V bias doesn't converge to the requested tolerance of 1E-06 in 200 steps. The detailed log file is attached

../ivcurve_0.10000V.log:| Calculation Converged in 165 steps |

../ivcurve_0.15000V.log:| Calculation Converged in 116 steps |

../ivcurve_0.20000V.log:| Calculation Converged in 123 steps |

../ivcurve_0.25000V.log:| Calculation Converged in 91 steps |

../trans_195612.log:| Calculation Converged in 21 steps |

../trans_195612.log:| Calculation Converged in 45 steps |

../trans_195612.log:| Calculation Converged in 147 steps

ivcurve_0.05000V.log:# Warning: The calculation did not converge to the requested tolerance! #

ivcurve_0.30000V.log:# Warning: The calculation did not converge to the requested tolerance! #

ivcurve_0.35000V.log:# Warning: The calculation did not converge to the requested tolerance! #

ivcurve_0.40000V.log:# Warning: The calculation did not converge to the requested tolerance! #