#TL;DR
The problem was caused by the capybara-helper
gem that installed another (newer) version of ChromeDriver.
We fixed it by disabling this gem on CircleCI with this modification to our Gemfile
:
gem 'chromedriver-helper' unless ENV.key?('CIRCLECI')
Then we had to rebuild without cache to fix this error:
Selenium::WebDriver::Error::WebDriverError:
unable to connect to chromedriver 127.0.0.1:9515