There are cases where thenuxt.config.js file is required for a deployment, not just the .nuxt folder.
We had, in addition to the node_modules production dependencies, only the .nuxt folder copied into our runtime docker container.
With the addition of
router: { base: '/app/' }we found that we also needed the nuxt.config.js or the files are served from / (but scripts would fail to load because the tags in the html try to load them from /app/...
Suggest keeping additional data such as router.base in the .nuxt output folder. (and/or update the documentation with guidance about keeping nuxt.config.js in production deployment packages).