Some customers use cookie deletion tools or other security measures, such as opening payment links in a separate browser. The result is that some orders are not registered even though the payment went through, or that the payment is made twice.
Do others also have this problem?
The interesting thing is that all customers say they rarely have any problems in other stores using PayPal.
I've already discussed with datakick but I am wondering whether others have this problem, too.
datakick's suggestion would be to implement some sort of auto-login functionality:
Save information about customer + cart into PayPal metadata when preparing payment
Retrieve these information when redirected back from PayPal
Verify that current context matches the stored metadata, or update context if they do not