How to delete multiple entries using Checkboxes? (PHP)

So i've been looking at a few resources on using multiple checkboxes as input. I'm building a PM system and want the user to be able to check off any message and then delete them with a button.

The problem is that whenever I check off any message(s):

A: You have to click the delete button twice.

B: Only the first message ever in the list ever gets deleted.

The button group:

<form method="post"
    <div class="button-group">
        <button type="submit" name="delete" class="delete button inbox">Delete</button>
        <button type="submit" name="mark" class="mark button inbox">Mark as Read</button>
    </div>

Later on the table rows:

<?php
    while ($row = mysqli_fetch_array($result)){?>
        <tr>
            <td><?php echo $row['PM_User1ID'];?></td>
            <td><?php echo $row['PM_User2ID'];?></td>
            <td><?php echo $row['PM_Subject'];?></td>
            <td><?php echo $row['PM_Timestamp'];?></td>
            <td>
                <label>
                    <input type="checkbox" name="check_list[]" value="<?php echo $row['PMID'];?>"><?php echo $row['PMID'];?>
                </label>
                </form>
            </td>
            <?php echo '<td><a name="'.$row['PMID'].'"href = "?link='.$row['PMID'].'">Reply</a></td>'; ?>
        </tr>
    <?php } ?>

And finally the Submit Post:

<?php
        if (isset ($_POST['delete'])){

            if(!empty($_POST['check_list'])){

                foreach($_POST['check_list'] as $selected){

                    $pmDelete = "DELETE FROM pm WHERE PMID = $selected"; 
                    $deletePM = $con->query($pmDelete);

                }
            }   
        }
    ?>

PM Page

GIF of issue