Having been happily using GitHub Actions to run my Rails/Rspec/Capybara tests for many months, it has now just stopped working!

The pipelines started failing on builds on 26th Aug, around 1200 GMT.
Eg clicking on a link that performs a POST, now does a GET.
(Using https://apidock.com/rails/ActionView/Helpers/UrlHelper/link_to “method: :post”)

Any test that requires JavaScript to run fails, eg :

    Failure/Error:
      page.accept_alert 'Are you sure?' do
        click_button('Create new application')
      end
Capybara::ModalNotFound:
  Unable to find modal dialog with Are you sure?
# ------------------
# --- Caused by: ---
# Selenium::WebDriver::Error::TimeoutError:
#   timed out after 20 seconds (no such alert
#     (Session info: headless chrome=84.0.4147.125))

The problem can be isolated from our code by looking at previous merges to our repo.
Older merges to master that passed at the time are now failing on re-runs.
It looks as if something changed in the base build on github actions?

Our config:

name: "Tests"
on:
  push:
jobs:

rspec:

name: RSpec

runs-on: ubuntu-latest

env:

RAILS_MASTER_KEY: ${{ secrets.RAILS_MASTER_KEY }}

RAILS_ENV: test

DATABASE_URL: postgres://postgres:postgres@localhost:5432/test

REDIS_URL: redis://localhost:6379/0
services:
  postgres:
    image: postgres:latest
    ports:
      - 5432:5432
    env:
      POSTGRES_PASSWORD: postgres
    options: >-
      --health-cmd pg_isready
      --health-interval 10s
      --health-timeout 5s
      --health-retries 5

  redis:
    image: redis:latest
    ports: ["6379:6379"]
    options: --entrypoint redis-server

steps:
  - uses: actions/checkout@v1

  - name: Setup ruby
    uses: ruby/setup-ruby@v1
    with:
      bundler-cache: true

  - name: Find yarn cache location
    id: yarn-cache
    run: echo "::set-output name=dir::$(yarn cache dir)"

  - name: JS package cache
    uses: actions/cache@v1
    with:
      path: ${{ steps.yarn-cache.outputs.dir }}
      key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
      restore-keys: |
        ${{ runner.os }}-yarn-

  - name: Install packages
    run: |
      yarn install --pure-lockfile

  - name: Install postgres client
    run: sudo apt-get install libpq-dev

  - name: Install dependencies
    run: |
      gem install bundler
      bundle install --path vendor/bundle --jobs 4 --retry 3

  - name: Create database
    run: |
      bundler exec rails db:create
      bundler exec rails db:migrate

  - name: Yarn
    run: yarn test

  - name: Run tests
    run: bundler exec rspec