Nightwatch can't launch chromium after upgrading to Ubuntu 19.10

My Nightwatch test suite was running just fine until I upgraded Ubuntu to 19.10. Now, when the browser launches from the test script I get an error message:

Failed to load extension from: . Manifest file is missing or unreadable

The Ubuntu install upgraded Chromium to 78.0.3904.70, and also switched to the snap version. I don't know which of these changes has caused the symptom I'm seeing.

I've upgraded chromedriver to match the same version as Chromium.

Chromium itself launches just fine as a browser, so the other solutions I've seen as search results, finding and deleting existing Chrome profiles, etc, I don't want to do. Ideally I'd like the browser that my nightwatch tests launch to be independent of any existing user profiles.

For reference, my Nightwatch config is:

// eslint-disable-next-line camelcase
const selenium_port = process.env.SELENIUM_PORT || 4444

const chromeArgs = process.env.SHOW_BROWSER ? [] : ['headless']

const driver = process.env.CHROMEDRIVER

module.exports = {
  page_objects_path: './tests/e2e/page-objects',
  test_settings: {
    default: {
      globals: {
        waitForConditionTimeout: 5000
      },
      selenium_port,
      desiredCapabilities: {
        browserName: 'chrome',
        chromeOptions: {
          args: chromeArgs
        }
      },
      webdriver: {
        server_path: driver
      }
    }
  },
  'selenium': {
    'port': selenium_port
  }
}