Reproduces an issue whereby a Worker is sometimes instantiated twice using webpack@5.
The messages App is rendering and Creating worker are always printed once, however Worker is running is sometimes printed twice. This may not be the first time the page loads and you may need to refresh the window/tab to reproduce this.
Note that this does not appear to only exist when running the dev server, production builds also exhibit this behavior.
Tested in Firefox 95.0.2 and Chrome 92.0.4515.107.