Hi there!
Can you let us know more information about this? Is this both the new order email to the customer, and the new order email to the site Admin?
Are you using PayPal Standard (the included PayPal option within WooCommerce), or a different option for your payment processing?
If you’re using PayPal Standard, it may be because you have both IPN and PDT enabled. If you could disable PDT, that should fix the issue (more info here: https://docs.woocommerce.com/document/paypal-standard/#section-29).
If you’re not using PayPal Standard, could you let us know what option you’re using, and also copy your System Status here?