Intermittent failure of jupyter labextension install

[tjcrone]

I have been working to build the Pangeo notebooks locally, and I have noticed that the base-notebook postBuild fails, only intermittently, during the jupyter labextension install:

Building jupyterlab assets (build:prod:minimize)
An error occured.
RuntimeError: JupyterLab failed to build
See the log file for details:  /tmp/jupyterlab-debug-pxded7y6.log
Removing intermediate container 5152aa5d766e
The command '/bin/sh -c ./binder/postBuild' returned a non-zero code: 1Traceback (most recent call last):
  File "build.py", line 183, in <module>
    main()
  File "build.py", line 168, in main
    r2d_build(
  File "build.py", line 85, in r2d_build
    r2d.build()
  File "/Users/tjc/miniconda3/envs/repo2docker/lib/python3.8/site-packages/repo2docker/app.py", line 700, in build
    raise docker.errors.BuildError(l["error"], build_log="")
docker.errors.BuildError: The command '/bin/sh -c ./binder/postBuild' returned a non-zero code: 1

But sometimes it works, sometimes it doesn't, with no changes to any of our code. It's pretty weird. I'm guessing some sort of network timeout from some server somewhere. Has anyone seen this?