It found bug with braintree paypal express. The braintree paypal express transaction still going true even i log out current paypal.
After login and redirect into checkout confirmation page, i open shopping cart page in another tab and re-click the paypal express button then log out. When press confirm the transaction on checkout confirmation page, the payment going true and showing checkout success instead redirect to shopping cart page.
It seem current registered form hash not in use to compare with new generate form hash. Any idea how to fix it?