Create a draft with the same slug as an existing post, the existing post will be 404.

[Toro_Unit]

Step-by-step reproduction instructions

1. create custom post type. and set 'show_in_rest' => true

<?php
function custom_init() {
        $args = array(
                'public' => true,
                'label'  => 'Books',
                'show_in_rest' => true,
        );
        register_post_type( 'book', $args );
}
add_action( 'init', 'custom_init' );

2. Publish new post of the post type.
3. Create draft post of the post type with same slug.
4. Go to the published post. but show draft post. if logged out, 404.

Using the block editor, a page can also create drafts with the same slug, which causes the same problem.

[h2ham]

It also happened in default posts.

1. Set permalink to %postname%.
2. Publish new post of default posts.
3. Create draft post of the default post with same slug.
4. Go to the published post. but show draft post. If logged out, 404.

[peterwilsoncc]

I've attempted to reproduce this on both 5.6 and trunk without success. I've tried with both a CPT per the original post and standard posts per the follow up comment.

Are either of you able to reproduce this with all plugins disabled and using a default theme such as Twenty Twenty-One?

[Toro_Unit]

@peterwilsoncc Thanks.

No plugins are used, and the theme is Twenty Twenty One. reproduced on WordPress 5.5 and 5.6.

When creating a post, please use the block editor.
Quick Edit or Classic Editor don't allow us to create a post with the same slug as an existing post.

[Toro_Unit]

A gif animation of the issue.

[Toro_Unit]

reproduced on page.