1.6 Blank Validation Page after payment and no Order in Prestashop

[Adam Smith BZ]

We have an issue that happens on only some orders where after the payment is taken the customer sees a blank validation page. The money is taken from the customers account but no order is registered on the Prestashop back end. 

We are using Prestashop 1.6.1.24 with HandePay payment module installed. This is the only payment method we have enabled. This issue happens to approximately every 1 in 10 orders, other orders go through fine. 

I have tried turning on debugging for Prestashop but it does not show any information on the blank validation page.  I have spoken with the merchant, HandePay, but they cannot see any issues their end. 

If anyone has any advice on what this issue could be or any troubleshooting steps then that would be appreciated. 

Thanks