Do you see the problem in any of our own demo galleries on this web page: http://www.juicebox.net/demos/ ?
Please try the Simple gallery (http://www.juicebox.net/demos/pro/simple) which has the thumbnails and captions positioned to the side of the gallery (somewhat similar to your own gallery).
If you do not see the problem in our own Simple demo gallery, then the problem may be unique to your own gallery or web page. Here are a few things you could try to see if they help:
(1) If possible, try using only alpha-numeric characters in your configURL's query string (or escape other characters such as spaces).
(2) Your dynamically-generated XML file is not seen by the browser as an XML file.
In your 'config.php' file, try adding the following code to set the file's header correctly:
<?php
header("Content-type: application/xml");
?>
(3) Also, there is no XML declaration at the top of the dynamically-generated XML file.
Make sure that your 'config.php' file outputs the following line of code at the very top of the dynamically-generated XML file:
<?xml version="1.0" encoding="UTF-8"?>
(4) Try clearing your browser's cache to ensure that your browser is fetching and using the most recent versions of your gallery files.
(5) It looks like you have renamed your gallery's 'jbcore' folder. Try uploading the complete stock Juicebox-Pro 'jbcore' folder to your web server (without renaming it or changing its structure) and load the 'juicebox.js' file from within it.
Hopefully one of the suggestions above will help. They may not make a difference but, they should all be fairly quick and easy to try.
If you do see the problem in our Simple demo gallery, then it sounds like a more generic issue with Juicebox and iOS 8.
If possible, please upload a couple of screenshots somewhere to demonstrate the problem so that I can pass them on to the developers if I need to submit a bug report. Thank you.