Jupyter-Lab: Kernel is died and restarting while show matplotlib plots

I'm trying to plot some cropped images of my data with matplotlib, but it always showing this message after running the code cell:

**the code snippest;**
```
import matplotlib.pyplot as plt
import numpy as np
#import helper

%matplotlib inline

def imshow(img):
npimg = img.numpy()
plt.imshow(np.transpose(npimg, (1, 2, 0)))

fig = plt.figure(figsize=(20, 4))
plot_size=20
for idx in np.arange(plot_size):
ax = fig.add_subplot(2, plot_size/2, idx+1, xticks=[], yticks=[])
imshow(images[idx])
```

Environment:
Jupyter-lab
Python 3.7
Conda environment: Base
matplotlib version: 3.3.4
OS: Windows 10 pro