Here pip tries to load pre-downloaded files.
Instead of using
pip install torch==1.8.0+cu111 torchvision==0.9.0+cu111 torchaudio===0.8.0 -f https://download.pytorch.org/whl/torch_stable.html

We use
pip --no-cache-dir install torch==1.8.0+cu111 torchvision==0.9.0+cu111 torchaudio===0.8.0 -f https://download.pytorch.org/whl/torch_stable.html --user

This overrides the pre-downloaded files and starts from scratch.