NextJS app directory return json data instead of a webpage.

### Before opening, please confirm:

- [X] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-hosting/blob/master/FAQ.md).
- [X] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-hosting/issues?q=is%3Aissue+).
- [X] I have read the guide for [submitting bug reports](https://github.com/aws-amplify/amplify-hosting/blob/master/CONTRIBUTING.md).
- [X] I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.
- [X] I have removed any sensitive information from my code snippets and submission.

### App Id

d97ykfklut38e

### AWS Region

ap-southeast-1

### Amplify Hosting feature

Not Applicable

### Frontend framework

Next.js

### Next.js version

13.4.5

### Next.js router

App Router

### Describe the bug

The server return JSON data instead of a web page html.

### Expected behavior

The server should return webpage html.

### Reproduction steps

- Visit https://www.techforhire.dev/
- Close the browser with the tab focused on https://www.techforhire.dev/
- Reopen the browser.

Here is a detailed video of how to recreate the issue.
https://photos.app.goo.gl/u7yp7CamFasdXgADA

### Build Settings

```yaml
version: 1
frontend:
phases:
preBuild:
commands:
- npm install
build:
commands:
- if [ "${AWS_BRANCH}" = "main" ]; then npm run build:prod; fi
- if [ "${AWS_BRANCH}" = "staging" ]; then npm run build; fi
artifacts:
baseDirectory: .next
files:
- '**/*'
cache:
paths:
- node_modules/**/*
```

### Log output

```
# Put your logs below this line

```

### Additional information

_No response_

Reproduce the behavior at https://www.techforhire.dev/ by closing and reopening the browser with the tab focused on the site. Review the supplied Amplify build settings and Next.js 13.4.5 App Router deployment, then compare the returned JSON with the expected webpage HTML; done means the site consistently returns HTML after reopening.

Written by the indexing model from the issue text.