Jquery progress bar preventing PHP file upload?

I had a PHP upload form for uploading video files to my server. It was working great until I added a Jquery/Ajax progress bar. The progress bar looks great and seems to work fine. The only issue is that after I added this code, my PHP isn't actually moving the files to my server, even though it was working just fine before I added the progress bar. Is there something I need to correct in the code so that the PHP uploads actually complete?

<!--Progress bar code -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script>
$(document).ready(function(){
    // File upload via Ajax
    $("#introUploadForm").on('submit', function(e){
        e.preventDefault();
        $.ajax({
            xhr: function() {
                var xhr = new window.XMLHttpRequest();
                xhr.upload.addEventListener("progress", function(evt) {
                    if (evt.lengthComputable) {
                        var percentComplete = Math.round(((evt.loaded / evt.total) * 100));
                        $(".progress-bar").width(percentComplete + '%');
                        $(".progress-bar").html(percentComplete+'%');
                    }
                }, false);
                return xhr;
            },
            type: 'POST',
            url: 'vidUpload.php',
            data: new FormData(this),
            contentType: false,
            cache: false,
            processData:false,
            beforeSend: function(){
                $(".progress-bar").width('0%');
                $('#uploadStatus').html('<img src="images/loading.gif"/>');
            },
            error:function(){
                $('#uploadStatus').html('<p style="color:#EA4335;">File upload failed, please try again.</p>');
            },
            success: function(resp){
                if(resp == 'ok'){
                    $('#uploadForm')[0].reset();
                    $('#uploadStatus').html('<p style="color:#28A74B;">File has uploaded successfully!</p>');
                }else if(resp == 'err'){
                    $('#uploadStatus').html('<p style="color:#EA4335;">Please select a valid file to upload.</p>');
                }
            }
        });
    });
    
});