Next.js experimental concurrentFeatures and rewrites don't work

This is a minimal reproduction of a bug where using experimental.concurrentFeatures prevents rewrites from working.

This app was bootstrapped via yarn create next-app, the additional meaningful changes are:

• Enable experimental features
• Install latest React, ReactDOM, and Next packages
• Add rewrites to next.config.js
• Add bar.js page (which /foo should render instead)
• Add _error.js page

Bug Reproduction:

• yarn
• yarn dev
• or:
  • yarn build
  • yarn start
• Visit localhost:3000

In Dev:

In dev (yarn dev), visiting localhost:3000/foo the page will hang and won't respond with any content.

Production:

In production, visiting localhost:3000/foo returns the _error.js page