Essentially your are saying any changes to the Iban number on the vendor bank inactivate the supplier and send and email?
I’d just start with the specific scenario that is not working and start from there.
Create an in trans data directive on the VendBank and monitor if the ibannumber changes from any to another stick a message on the true condition to help you work out the logic.
You can also use the change at the same time to track that change also, as well as calling the post processing directive and send the email.
I think this is one of those situations where using code, just overcomplicates it and we need to take a page from @JasonMcD book of low codedness.
There’s a tidbit in this post below on formatting your code to make it more readable for your helpers.
Tips for asking question on the forum - Experts’ Corner - Epicor User Help Forum
Hope that helps