Hi,
Thank you, we got your emails.
What happened is really strange, especially the fact that the same email was sent to the correct email address both before and after the email that was sent to the wrong email address.
So I suspect that there is indeed something dynamically changing the email address for some reason. It's likely a bug somewhere or something wrongly configured.
Did it happen only for one email or did it happen several times ?
I don't think that 503 errors have anything to do with that nor that error message.
First, to be able to identify the problem, the thing that should be done would be to be able to reproduce the issue consistently. There must be something different between that order with the issue and the other orders. If it only happened with one order so far, I would recommend to wait and monitor the next orders to see if you have the issue again and try to find similarities between the orders with the issue compared to the other orders.
Once you get more information on the issue, it will help us understand better the situation and hopefully provide a solution.