In Create React App 4.0,
react-refresh was added.
However, this experimental feature causes the page to no longer hot reload when files like
index.js are edited and saved (see #9984).
The fix is to disable the environment variable
# .env FAST_REFRESH=false
This can be done using bash in the command-line:
echo 'FAST_REFRESH=false' >> .env
Once you restart your development server, edits to
index.js should trigger an automatic page refresh!