Prestashop > Worldpay > Google Analytics order transaction issues

[pjm:digital]

I work with a client who runs their site on Prestashop (v. 1.6.1.14). They use Worldpay for card payments which is connected via 0.7z module - alongside Paypal. They use Google Analytics.

Recently we've had more and more transactions missing from Google Analytics reporting. After much investigation, it appears to be ALL Worldpay transactions. 

I've contacted Worldpay who confirm they have not changed anything, nor have they had any issues reported from other customers. We've spent a long time trying different things, and have been through the WP admin with them step by step to confirm everything is as it should be. 

From a front end use point of view, there is a delay on WP confirmation page before it redirects to our website - we've tried to explain with them to remove this WP confirmation step as it's probably part of the issue, as well as being not very user friendly - but we've now hit a bit of a roadblock with them.

All our Paypal transactions are ok.

Anyone experienced similar and how did you resolve?