Our store runs Expresso Store 2.5.1 on EE 2.10.1
Checkout is via Paypal Express.
Certain orders go off for payment via Paypal and the order system records a successful payment and the status in the database for the order is 'New' (as expected) however when viewing the orders in the admin, the status shown is 'incomplete'. The option to print invoice also doesn't then work. The order (or more accurately 'the cart' as it isn't technically marked as an order yet) shows the successful payment from Paypal.
I'm guessing that this could be because a user hasn't left Paypal and gone to the order success page thereby not generating the URL and leaving the order unconfirmed?
If anyone can suggest a reason as to how this can happen and more importantly, how to avoid it?