Predefined 404 (‘Page not found’) block too small

Hi Sven,

I’m not sure how that happened, but we can take a closer look at the settings if you’re able to provide a temporary admin login.

Alternatively, you can try this CSS, which should fix the layout:

.error404 #post-3496.generate-columns {
    width: 100%;
}

Hi Sven,

The cause is your permalink structure (/blog/%postname%/). Because your post URLs sit under a /blog/ base, a non-existent URL in that path gets parsed as the blog/posts context before WordPress falls through to the 404. The result is that the main query is populated with real posts on the 404 page, so your blog column/masonry settings apply to it — which is why the 404 content ends up inside a grid-33 column with the grid-sizer element, and why it only “fixes” itself when you narrow the window and hit the mobile breakpoint.

It’s not the 404 template inheriting a grid; it’s the populated query running through your blog columns layout.

You can disable columns specifically on the 404 by adding this to a code snippet (or your child theme’s functions.php):

add_filter( 'option_generate_blog_settings', function ( $options ) {
    if ( is_404() ) {
        $options['column_layout']   = false;
        $options['masonry']         = false;
        $options['featured_column'] = false;
    }
    return $options;
} );

That forces the 404 to render full width regardless of your blog column settings.

Adding PHP

Hi Sven,

I traced this to the exact cause in GeneratePress’s blog module.

When you request a non-existent URL at the site root (/test123), WordPress correctly flags it as a 404 and displays your 404 template — but it also runs the main posts query first, and that query comes back holding posts. Those posts are never displayed (the 404 template doesn’t loop over them, which is why you don’t see any posts on the page), but they’re still sitting in the query.

GeneratePress decides whether to wrap the content in its column/masonry layout by checking the current post type. Because the query is holding posts, that check passes — so the column wrapper (the grid-sizer element and grid-33 width) gets added around your 404 content, even though no posts are shown.

A non-existent URL under your blog base (/blog/test123) returns an empty query, so that check finds nothing, and the 404 renders correctly at full width. That’s the entire difference between the two.

Disabling columns specifically on 404s is the right fix. The snippet you applied handles it. As a more targeted alternative, this filter does the same thing:

add_filter( 'generate_blog_columns', function ( $columns ) {
    return is_404() ? false : $columns;
} );

Ok, Sven, no problem!