Steps for reproducing

1. Install ruby dependencies

bundle install

2. Install js dependencies

yarn install

3. Setup sqlite db

rails db:create
rails db:migrate

4. Run the app

rails s

5. Click on the "Add timer" button

You should see the previously added timers reset their local state because the React root is being re-created and the following warning on the console:

Warning: You are calling ReactDOMClient.createRoot() on a container that has already been passed to createRoot() before. Instead, call root.render() on the existing root instead if you want to update it.