从HTML代码示例中很难理解您想要实现什么，但通过php，您可以执行以下操作。

<?php
$posts = new WP_Query([
    \'post_type\'      => \'services\',
    \'posts_per_page\' => -1,
    \'order\'          => \'ASC\'
]);

if ($posts->have_posts()) :
?>
<ul class="slider-container">
    <?php
    $loop_position = 1;
    while ($posts->have_posts()) {
        $posts->the_post();

        // if loop position is greater than our threshold (8) reset to initial position (1)
        if ($loop_position > 8) $loop_position = 1;

        // if we are in the first loop (loop position 1) itiration create the slide open tag
        if ($loop_position === 1) echo \'<li class="single-slide">\';

        // if we are in the first/fifth loop (loop position 1/5) itiration create the row open tag
        if (in_array($loop_position, [1,5])) echo \'<div class="row">\';

        // here we can simply output each loop itiration html as we need
        echo \'<div class="col-md-3">\';
        echo     \'<div class="box-desc">\';
        echo         "<h4>Some title {$loop_position}</h4>";
        echo     \'</div>\';
        echo \'</div>\';

        // if we reached the end of the loop (no more post) we need to close all the tags
        // starting from row than single-slide
        if ($posts->found_posts == $loop_position) {
           echo \'</div></li>\';
           
           // to prevent the rest of the code from executing we exit out of the loop, using break
           break;
        }

        // if we are in the fourth/eighth loop (loop position 4/8) itiration create the row closing tag
        if (in_array($loop_position, [4,8])) echo \'</div>\';

        // if we are in the last loop (loop position 8) itiration create the slide closing tag
        if ($loop_position === 8) echo \'</li>\';

        // increate loop position by 1
        $loop_position++;
    }
    ?>
</ul>
<?php
endif;
wp_reset_postdata();
?>

HTML输出如下

<ul class="slider-container">
    <li class="single-slide">
        <div class="row">
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 1</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 2</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 3</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 4</h4>
                </div>
            </div>
        </div>
        <div class="row">
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 5</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 6</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 7</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 8</h4>
                </div>
            </div>
        </div>
    </li>
    <li class="single-slide">
        <div class="row">
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 1</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 2</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 3</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 4</h4>
                </div>
            </div>
        </div>
        <div class="row">
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 5</h4>
                </div>
            </div>
            <div class="col-md-3">
                <div class="box-desc">
                    <h4>Some title 6</h4>
                </div>
            </div>
        </div>
    </li>
</ul>

正如我们决定的那样，每八（8）个帖子都会收到自己的幻灯片，在每个幻灯片中，每四（4）个帖子都会用<div class="row">...</div> 标签

我个人认为这有点过分了，太复杂了，你可以不使用引导程序来布局，而使用css来达到同样的效果grid.

如果您愿意，我可以编辑我的答案以包括非引导布局