从评论中的讨论到您的问题，下面是我的建议和建议

只是为了在建设性的回答中概括并添加所有内容

在tag 中的参数WP_Query 接受条款slug, 不是name

始终重置自定义WP_Query, 总是利用wp_reset_postdata() 查询完成后，就在endif

您不能使用tag 作为您的短代码名称，它是reserved name 在Wordpress中

我相信你做事的顺序是导致你头痛的原因。此外，短代码应该return 其输出，而不是echo 信息技术看看Shortcode API 关于如何创建短代码

在检查代码中的任何内容或帖子是否有标记之前，实际上必须先获取当前帖子。没有这个，您的代码将无法工作。所以，首先要做的是打电话给您的全球$post. 一旦你有了它，你就可以把ID传给get_the_tags

完成后，您的代码应该可以正常工作

下面是一个示例：（警告：未测试）

add_shortcode(\'shortcodetag\', \'tags\');
function tags() {
    ob_start();
    global $post;

    $posttags = get_the_tags( $post->ID );
   if ( $posttags ) 
    {
        // Loop for each tag the custom post has
        foreach($posttags as $tag) 
        {
            $tag_name = ($tag->slug);

            // Search for posts with the same tag,
            // is a custom type and don\'t return
            // the current post
            $args = array(
                \'post_type\' => \'custom_post\',
                \'tag\' => $tag_name,
                \'post__not_in\' => array( $post->ID )
                );

            $query = new WP_Query( $args );

            // Make sure we got results
            if( $query->have_posts() ) 
            {
                // Loop through each returned post
                while ( $query->have_posts() )
                {
                    $query->the_post(); // Returns null

                    //LOOP ELEMENTS

                }
                wp_reset_postdata();
            }
        }
    }

     $myvariable = ob_get_clean();

     return $myvariable;

}

EDIT

function tags() {
global $post;

$posttags = get_the_tags( $post->ID );
   if ( $posttags ) 
    {
        // Loop for each tag the custom post has
        foreach($posttags as $tag) 
        {
            $tag_name = $tag->slug;

            // Search for posts with the same tag,
            // is a custom type and don\'t return
            // the current post
            $args = array(
                \'post_type\' => \'custom_post\',
                \'tag\' => $tag_name,
                \'post__not_in\' => array( $post->ID )
                );

            $query = new WP_Query( $args );

            // Make sure we got results
            if( $query->have_posts() ) 
            {
                // Loop through each returned post
                while ( $query->have_posts() )
                {
                    $query->the_post(); // Returns null
                        //LOOP ELEMENTS
                    the_title(); //display post title
                    if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
                        the_post_thumbnail(); //display the featured image
                    } 
                    the_content(); //displays the post\'s content

                }
wp_reset_postdata();
            }
        }
    }
}