sitespeed.io: Cannot read property 'timings' of undefined

We’re getting an error on a complicated script only when -n is greater than 1. With -n 1 the script appears to work and the output html reports look good.

2019-02-05 18:21:53] ERROR: [sitespeedio.queuehandler] TypeError: Cannot read property ‘timings’ of undefined at addExtraFieldsToHar (/usr/src/app/node_modules/browsertime/lib/core/engine/index.js:70:27) at Engine.runByScript (/usr/src/app/node_modules/browsertime/lib/core/engine/index.js:164:7)

Not exactly sure what the problem is, still trying to prune it down to an example we can share publicly. The docker command being used is:

docker run --shm-size=1g --rm -v “$(pwd)”:/sitespeed.io sitespeedio/sitespeed.io:8.2.2 --multi --spa -n 2 -v urt1.js

where urt1.js consists of (all commands are shown, but non-public parameters are omitted)

module.exports = async function(context, commands) {
    await commands.measure.start('https://internal-host.com');

    await commands.measure.start('navigate_to_login');
    await commands.click.byClassNameAndWait('my-login-button-classname');
    await commands.measure.stop();

    await commands.measure.start('do_login');
    await commands.addText.byXpath('username,'.//a-real-xpath');
    await commands.addText.byXpath('password','.//a-real-xpath');
    await commands.click.byId('sign_in');
    await commands.wait.byXpath('.//a-real-xpath-to-something-that-appears-after-login', 20000);
    return commands.measure.stop();
}

Is there anything suspicious about this general sequence of commands? Thanks, Don