Chrome "Take Heap Snapshot" never completes

Summary:

I'm trying use Chrome's "Take Heap Snapshot" to track down a memory leak in some node.js code, but the act of taking a snapshot never completes.

Am I mis-using the tool somehow?

Details:

Here's the node.js app:

#!/usr/bin/env node

var serialserver = require('./p5.serialserver');
serialserver.start();
console.log("p5.serialserver is running");

Here's how I invoke it, and what it prints out:

$ node --inspect ./p5serial
Debugger listening on port 9229.
Warning: This is an experimental feature and could change at any time.
To start debugging, open the following URL in Chrome:
     chrome-devtools://devtools/remote/serve_file/@521e5b7e2b7cc66b4006a8a54cb9c4e57494a5ef/inspector.html?experiments=true&v8only=true&ws=localhost:9229/node
p5.serialserver is running

In Chrome (Version 59.0.3071.115), running under OSX 10.12.6 (Sierra), I open the given URL and click on Take Heap Snapshot. I see the icon in the left column which says:

Snapshot 1
Snapshotting...

... but even after waiting for ten minutes, the snapshot hasn't completed. This is not a particularly large node application.

What am I missing?