When running in dev-mode it renders the following warning to the browser console:
emotion-react.browser.esm.js:398 You are loading @emotion/react when it is already loaded. Running multiple instances may cause problems. This can happen if multiple versions are used, or if multiple builds of the same version are used.
It seems that both:
emotion-react.cjs.dev.jsemotion-react.browser.esm.js
are included into the browser bundles.
While 1. is bundled with the dependencies, 2. is loaded by the actual application as an ESM module.