getStaticProps with { fallback: true } is very slow when spa routing.

Bug report

Describe the bug

getStaticProps with fallback: true, NextJS send json response to client after calling getStaticProps in server. In my case it takes 2s until the json response comes to browser in vercel production environment in spite of getStatipProps finishing in 100ms. This may be caused by the json response is sent after the ssg rendering in server, I think the json must be returned just after getStatiProps finished.

To Reproduce

1. Use getStatipProps and getStaticPaths with fallback: true
2. Request ssg page from browser.
3. When ssg page loaded, navigate to another dynamic routing page with next/link or next/router.
4. See the chrome dev tool to see network response.

Expected behavior

The json response returned just after getStaticProps finished in server, and SSG redering and caching is done in server after that.

Screenshots

System information

• OS: macOS, Vercel server.
• Browser (if applies): chrome
• Version of Next.js: 9.4.2
• Version of Node.js: latest

[remyb-dev]

Still the same problem with next 12.0.1 very slow in dev when getStaticPaths is used in a page.

[alepacheco]

This is still an ongoing issue, any update?