I have the same error, in my case:

CUDA 11.0 on A100
Conda environment with

python -m pip install torch==1.7.0+cu110 torchvision==0.8.1+cu110 torchaudio==0.7.0


Apex using the lastest from repo
I have tried all python version 3.6,7,8
=> Are there anyone have solved this problem  , I test with many pytorch from source but nothing change, I think this is from Cuda11.0 because I have tried my source code successfully on V100 Cuda10.2