Unable To Create zip for multiple large files and unlink the zip

Question

I am trying to download some files from server using a php script but when I execute the script it works fine with smaller number of file with lesser number of files to zip however when I try execution with larger no of files the server times out and also the zip generated as the result is not deleted and occupies the space on server. the php script is as follows

if(isset($_POST['download_all']))
{ 
    $errmsg = '';
    $sql = mysqli_query($conn, "select * from img WHERE gal_id = '".base64_decode($_REQUEST['Gal'])."' And uid='".$_SESSION['uid']."' order by image1 asc");
    $url = "dataroot/Gallery/".base64_decode($_REQUEST['Gal'])."_".$_SESSION['uid']."/";
    while($res = mysqli_fetch_array($sql)){  
      $filess[] = $url.$res['image1']; 
      echo $url.$res['image1'];
    }  
$files = json_encode($filess);
$files = json_decode($files);

if(is_array($files)) {
    foreach($files as $file) {
        if(file_exists($file)) {
            $valid_files[] = $file;
        }
    }
}

if(count($valid_files > 0)){
    $zip = new ZipArchive();
    $zip_name = "total.zip";
    if($zip->open($zip_name, ZIPARCHIVE::CREATE)!==TRUE){
        $error .= "* Sorry ZIP creation failed at this time";
    }

    foreach($valid_files as $file){
        $zip->addFile($file);
    }

    $zip->close();
    if(file_exists($zip_name)){
        // force to download the zip
        header("Pragma: public");
        header("Expires: 0");
        header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
        header("Content-Transfer-Encoding: binary");
        header("Content-length: $ size");
        header("Cache-Control: private",false);
        header('Content-type: application/zip');
        header('Content-Disposition: attachment; filename="'.$zip_name.'"');
        ob_clean();
        flush();
        readfile($zip_name);
        ignore_user_abort(true);
     //remove zip file from temp path
        unlink($zip_name);
    }

} else {
    echo "No valid files to zip";
    exit;
}

}

I have updated the memory and timeout setting on the server. The issue persists. Also the zip thus formed as the result is not unlinked and consumes memory on server.

already referred to Reading very large files in PHP and How to download multiple large files with php?

but unable to resolve the issue.