We've been receiving multiple reports of missing and delayed transactions in the past few hours and we're looking into the issue. So far it appears to be delays on PayPal's end but we are still investigating.

PayPal has confirmed the delays and they are working to resolve the problem:

https://www.paypal-status.com/history/eventdetails/81502

PayPal is no longer reporting any issues so all orders should be processing as normal now.