Link to the code that reproduces this issue

https://github.com/heecheon92/next15-test

To Reproduce

Local Build,

1. npm i && npm run dev (or npm run start)

2. visit localhost:3000

3. visit the page -> Route Interception (or you can simply visit localhost:3000/playground/route_interception/home)

4. Visit "Progress" tab from "Home" tab. (It displays as normal page)

5. Visit "Progress" tab from "Payment" tab. (It displays as modal)

6. deploy the product on vercel.

7. visit the page -> Route Interception (or you can simply visit https://next15-test-gilt.vercel.app/playground/route_interception/home)

8. Visit "Progress" tab from "Home" tab. (It should display as normal page)

9. Visit "Progress" tab from "Payment" tab. (It should display as modal but it displays as normal page)

Current vs. Expected behavior

In local development and production build, intercepting & parallel route behaves as expected.

In local builds, regardless of dev or prod, visiting "Progress" tab from "Payment" tab display as modal.

Once deployed to vercel, visiting "Progress" tab from "Payment" tab displays as normal page.

It should be displayed as modal just like local build.

Provide environment information

Operating System:
  Platform: darwin
  Arch: x64
  Version: Darwin Kernel Version 24.1.0: Thu Oct 10 21:02:27 PDT 2024; root:xnu-11215.41.3~2/RELEASE_X86_64
  Available memory (MB): 16384
  Available CPU cores: 12
Binaries:
  Node: 20.10.0
  npm: 10.9.0
  Yarn: 1.22.21
  pnpm: 9.7.1
Relevant Packages:
  next: 15.1.4 // Latest available version is detected (15.1.4).
  eslint-config-next: 15.1.4
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.7.2
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Parallel & Intercepting Routes

Which stage(s) are affected? (Select all that apply)

Vercel (Deployed)

Additional context

One weird behavior pertaining to this issue is that "prefetch" on Link component is speculatively related.

From the sample project I provided, if you explicitly set prefetch option to "false" on Link to "Progress" tab, like this

          <Link
            href="/playground/route_interception/progress"
            className="p-2 bg-blue-600 text-white rounded-md"
            prefetch={false}      // <-- this option
          >
            Progress
          </Link>

This partially fixes the issue.

In detail, when prefetch is set to false and deployed to vercel, following happens

1. Visit following pages with exact order "Home" -> "Payment" -> "Progress"
2. Progress page displays as modal just like local build
3. Close the modal, visit "Home" again and then visit "Progress"
4. Now, Progress page shows "404 page not found"

Following page is built on exactly same source code but prefetch option for the Link to Progress page is set to false.

https://next15-test-git-prefetchdisabled-heecheon92s-projects.vercel.app/playground/route_interception/home