Yes, I was able to get this resolved.
For me, the issue went away when I spun up a new EC2 instance and used the default PyTorch 3.6 virtual environment.
So I must have messed something up when I was doing package installation including perhaps my installation of PyTorch.
FWIW here are the current details in my env (p3.2xlarge, Ubuntu 18.04, Deep Learning AMI):
Platform Linux-4.15.0-1057-aws-x86_64-with-debian-buster-sid
Python 3.6.5 |Anaconda, Inc.| (default, Apr 29 2018, 16:14:56)
[GCC 7.2.0]
PyTorch 1.3.1