https://nuxtjs.org/api/configuration-router/#extendroutes not working with nuxt generate. I'm working on a fix, will attach the pull request here once done.
<!--cmty--><!--cmty_prevent_hook--><div align="right"><sub><em>This bug report is available on <a href="https://nuxtjs.cmty.io">Nuxt.js</a> community (<a href="https://nuxtjs.cmty.io/nuxt/nuxt.js/issues/c237">#c237</a>)</em></sub></div>