PayPal transactions are routing to a deleted instance and I can't change it - why?

Let's imagine a scenario where you setup gateway routing for a PayPal gateway --> Subscribed several customers via that gateway --> Delete the gateway --> Notice that recurring payments are no longer processing and are still being sent to the old gateway. How can you fix this?

PayPal billing agreements can only be processed through the PayPal account where they were originally created. In this scenario, if the billing agreement the merchant is using was originally created through the deleted PayPal instance, it will continue to route through that original gateway. If you have updated your PayPal gateway account with a new account, you'll need to have the customer update their PayPal billing information on record so that a new billing agreement can be generated through the new PayPal gateway.