Style Transfer produces white noise

I’m playing with Neural Transfer Using PyTorch — PyTorch Tutorials 1.9.0+cu102 documentation
Running this demo on colab (torch version == 1.9.0)
I changed images (style is and content is
Also set num_steps to 1500
After a while (about 1400 steps) image degrades to white noise

Below is Content and Style losses graph to show this.

Why is it happening?