Thanks for your response @ptrblck.
My Dataset code is perhaps too long to post in a ‘message’, but here’s a link:  https://github.com/drscotthawley/signaltrain/blob/master/signaltrain/datasets.py 30   Actually, this file contains two different versions to use for Dataset, and the same error occurs for both.
My Dataset code is all numpy; the only PyTorch-specific code is
“from torch.utils.data import Dataset” and the definition of my Dataset.   …So I can’t see how any CUDATensors could be getting initialized.
One other thought I had was: I wondered if maybe NVIDIA’s Apex Mixed-Precision system might be affecting things somehow, so I turned that off. Same error message.
SOLUTION!!:* Without changing my code at all, I downgraded PyTorch 1.2.0 to 1.0.1, and now my code is running fine again with no errors:
$ conda install pytorch=1.0.1 -c pytorch 
Collecting package metadata (repodata.json): done
Solving environment: done

## Package Plan ##

  environment location: /home/myusername/anaconda3/envs/myenv

  added / updated specs:
    - pytorch=1.0.1


The following packages will be SUPERSEDED by a higher-priority channel:

  torchvision        pytorch/linux-64::torchvision-0.4.0-p~ --> pytorch/noarch::torchvision-0.2.2-py_3

The following packages will be DOWNGRADED:

  pytorch             1.2.0-py3.7_cuda10.0.130_cudnn7.6.2_0 --> 1.0.1-py3.7_cuda10.0.130_cudnn7.4.2_2



Any ideas as to what might have changed in newer versions of PyTorch that ‘broke’ my code?
Thanks.