Paypal cancels order when transaction id returns

-- HikaShop version -- : 2.6.1

Hi There,

When a customer places an order using paypal as the payment method, in SOME cases, and i cannot see any differences, the paypal plugin will cancel the order as an invalid status when paypal returns the transaction id.

In some cases, the order confirms correctly, but i cannot see any difference between an order which paypal returns as invalid, and one where the return is confirmed.

Any help would be appreciated!

Hikashop Paypal Payment Plugin settings:

Invalid Status: cancelled
Allow Payment notifications from paypal: Yes
Pending Status: Payment Pending
Verified Status: Confirmed
Return Method: Yes

Example from order history: (sensitive data removed, see attachment for screenshot)
payment cancelled automatic payment notification received xxx.xxx.xxx.xxx 2016-02-20 12:09 PayPal transaction id: xxxxxxxxxxxxx
creation created Order created / xxx.xxx.xxx.xxx 2016-02-20 12:08