Gets error 404 in preview page

[davidperez]

In latest version of WordPress 6.4.1, we get error 404. It redirects to a undefined page.

For example link preview:
/wp-admin/post.php?post=34891&action=edit

Gets:
/wp-admin/undefined

We are using Classic Theme (GeneratePress) and we've tried with latest version of Gutenberg. But we have tried without plugins and other Theme like Twentytwenty four.

[cbravobernal]

Hi David,

Thank you for addressing the issue. Unfortunately, I am unable to replicate it despite my efforts:

I tested it in my local environment, utilizing PHP 8.1.23, MySQL 8.0.16, and WP 6.4.1.

I created several posts and navigated to ​http://generate.local/wp-admin/post.php?post=8&action=edit.

I activated the GeneratePress theme and Gutenberg.

Checked ​http://generate.local/?p=8&preview=true, and it appears to be functioning correctly.
Additionally, I tested it without GeneratePress and Gutenberg, and it still functions flawlessly in my environment.

Could you please provide further details?

Best regards.

[luckybhumkar]

Thanks, @davidperez for bringing attention to this strange bug.

I too facing the same issue with two websites. In my case,

1. Draft Post > Preview in new tab > Does not work (Redirect to Undefined page)

2. Published Post > Preview in the new tab > Works

3. All posts list > Preview > Works

[jorbin]

I think this may be a duplicate of #59915.

[manishchopra]

Reproduction Report

Description

Attempted to reproduce the issue: 404 error on preview page.

Environment

• WordPress: 6.8.2
• PHP: 8.3.24-dev
• Server: PHP.wasm
• Database: WP_SQLite_Driver (Server: 5.5 / Client: 3.40.1)
• Browser: Chrome 139.0.0.0
• OS: Windows 10/11
• Theme: GeneratePress 3.6.0
• MU Plugins:
  • rewrite.php
• Plugins:
  • Gutenberg 21.4.0

Actual Results

1. ❌ The issue could not be reproduced.
2. ❌ Preview worked as expected without redirecting to /wp-admin/undefined

Steps Taken to Reproduce

1. Installed and activated the Gutenberg plugin.
2. Installed and activated the GeneratePress theme.
3. Created a new post → Edit → Chose Preview in New Tab → Preview loaded correctly (no /wp-admin/undefined).
4. Repeated steps described by @luckybhumkar: Drafted a post > Preview in new tab Still did not redirect to an undefined page.

[SirLouen]

@davidperez can you still reproduce this nowadays?

[davidperez]

Hello, Thanks for your replies. I didn't see the problem after updates, so we can close this ticket.

[luckybhumkar]

@manishchopra, I appreciate your effort. I agree with @davidperez; the problem no longer exists, and we can close this ticket.

[SirLouen]

Time to close it then!