Capybara Selenium-webdriver Net::ReadTimeout when using RSpec file fixtures

I'm noticing a strange issue that I haven't been able to solve for a few days.

I have a Rails 5 API server with system tests using RSpec and Capybara + Selenium-webdriver driving headless Chrome.

I'm using Capybara.app_host = 'http://localhost:4200' to make the tests hit a separate development server which is running an Ember front-end. The Ember front-end looks at the user agent to know to then send requests to the Rails API test database.

All the tests run fine except for ones which use RSpec file fixtures.

Here's a stripped down example:

describe 'the feature', :vcr, type: :system do
  fixtures :all

  before do
    Capybara.session_name = :a_user
    visit('/') # This hangs, ends with `Net::ReadTimeout` sometimes.
    ..
  end

  it 'can use the feature' do
    ..
  end
end

This will fail maybe 99% of the time. There is the odd case where it passes. I can get my test suite to eventually pass by running it on a loop for a day.

I ended up upgrading all versions to the latest (Node 10, latest Ember, latest Rails) but the issue persists.

I can post a sample repo that reproduces the issue later. I just wanted to get this posted in case anyone has encountered the issue.

Here's a typical stack trace when the timeout happens:

 1.1) Failure/Error: page.evaluate_script('window.location.reload()')

      Net::ReadTimeout:
        Net::ReadTimeout



      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/webmock-3.3.0/lib/webmock/http_lib_adapters/net_http.rb:97:in `block in request'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/webmock-3.3.0/lib/webmock/http_lib_adapters/net_http.rb:110:in `block in request'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/webmock-3.3.0/lib/webmock/http_lib_adapters/net_http.rb:109:in `request'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.14.0/lib/selenium/webdriver/remote/http/default.rb:121:in `response_for'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.14.0/lib/selenium/webdriver/remote/http/default.rb:76:in `request'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.14.0/lib/selenium/webdriver/remote/http/common.rb:62:in `call'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.14.0/lib/selenium/webdriver/remote/bridge.rb:164:in `execute'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.14.0/lib/selenium/webdriver/remote/oss/bridge.rb:584:in `execute'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.14.0/lib/selenium/webdriver/remote/oss/bridge.rb:267:in `execute_script'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.14.0/lib/selenium/webdriver/common/driver.rb:211:in `execute_script'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/capybara-3.8.2/lib/capybara/selenium/driver.rb:84:in `execute_script'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/capybara-3.8.2/lib/capybara/selenium/driver.rb:88:in `evaluate_script'
      # /home/mhluska/.rvm/gems/ruby-2.5.1/gems/capybara-3.8.2/lib/capybara/session.rb:575:in `evaluate_script'
      # ./spec/support/selenium.rb:48:in `refresh'
      # ./spec/support/pages.rb:70:in `signup_and_verify_email'
      # ./spec/system/payment_spec.rb:43:in `block (3 levels) in <top (required)>'

I should point out it doesn't always happen with page.evaluate_script('window.location.reload()'). It can happen with something benign like visit('/').