Payments no longer marking as Processing

I recently had a server upgrade to Apache 2.4 and PHP 5.6 and since then my clients JigoShop site using the SagePay Form payment processor no longer completes the order properly.

When the customer returns to the site after paying at SagePay they are presented with a blank white page with just the number 1 at the top.

I’ve tried downgrading the PHP version to 5.4 but it’s still doing the same.

I’d rather not have to downgrade the whole lot to PHP 5.2 and Apache 2.2 if at all possible (back to it’s previous state).

Here’ the system setup:

Home URL: https://www.emptybox.co.uk
Site URL: https://www.emptybox.co.uk
Jigoshop Version: 1.17.7
Jigoshop Database Version: 1503180
Log Directory Writable: ? To allow logging

WP Version: 4.3
WP Multisite: –
WP Memory Limit: 64 MB
WP Debug Mode: –
Language: en_US

### Server Environment ###

Server Info: Apache
PHP Version: 5.4.45
PHP Post Max Size: 20 MB
PHP Time Limit: 600
PHP Max Input Vars: 1000
SUHOSIN Installed:
MySQL Version: 5.5.42
eAccelerator: ?
APC: ?
OpCache: ?
Short Open Tag:
Allow URL fopen:
Session:
Cookie Path: /
Save Path: /tmp
Use Cookies:
Use Only Cookies:
Max Upload Size: 20 MB
Default Timezone is UTC:
fsockopen/cURL:
SoapClient:
Remote Post:
Remote Get:

https://www.ads-software.com/plugins/jigoshop/