'npm install' suddenly failing

I have built my system 90+ times and today I am encountering an ‘npm install’ failure:

https://circleci.com/gh/radgrad/datamodel/94

I have many previous builds where npm install worked fine:

https://circleci.com/gh/radgrad/datamodel/tree/master

As far as I know, I have not modified anything with respect to npm or the build environment. I’ve tried rebuilding without caching, but this did not fix anything. npm does not appear to be down according to its status page.

How do I diagnose this problem? Thank you.

Not sure why, but a few hours later I started a rebuild and this time the ‘npm install’ step worked. Some kind of intermittent network connectivity issue?