Hi KFrank,
thanks for reporting this issue. I seem to run into the same error and I guess the download is failing somehow.
Downloading and Extracting Packages
lz4-c-1.9.3          | 186 KB    | ######################################################################################################################################################################## | 100%
pytorch-1.8.0.dev202 | 873.5 MB  |                                                                                                                                                                          |   0%
torchaudio-0.8.0.dev | 14.2 MB   | ######################################################################################################################################################################## | 100%
torchvision-0.9.0.de | 26.2 MB   | ######################################################################################################################################################################## | 100%

InvalidArchiveError('Error with archive .../pytorch-1.8.0.dev20210122-py3.8_cuda11.0.221_cudnn8.0.5_0.tar.bz2.  You probably need to delete and re-download or re-create this file.  Message from libarchive was:\n\nSeek failed')

The file itself is available here 15 and wget yields a slow download speed of ~500kB/s.
I’m unsure, if conda uses some timeouts or what the reason is.
@seemethere do you have an idea and can reproduce it?
PS: I’m using a new conda env with Python=3.8.
UPDATE:
downloading the file manually and installing it via conda install ./pytorch-1.8..... also fails with the same error, so it doesn’t seem to be related to a timeout.
Unpacking the .tar.bz also works fine without an issue using tar xvf.
UPDATE2:
It seems to be a known issue 20 in conda-package-handling with a potential PR 10.