Unable to understand EIS with pybamm-eis

[YadulSethi]

Hi Ferran brosaplanella,
I am doing impedance with the pybamm-eis module of a symmetric cell where both the positive and negative electrode parameters identical. I have specifically change the opencircuit voltage parameter to a constant value (u_eq=0.8) and I expect low-frequnecy impedace to be a real value and imaginary part to be zero, since OCV is a constant value. However I get a increasing imaginary part at very low frequnecy. Below is the code that I am using::
import pybammeis
import pybamm
import numpy as np
import matplotlib.pyplot as plt

DFN with capacitance

model = pybamm.lithium_ion.DFN()
para_v = pybamm.ParameterValues("Chen2020")
print(para_v)
eis_sim = pybammeis.EISSimulation(model,parameter_values=para_v)

It would be very nice if you could help me figure out the issue?