Here's what our team has decided to do in case anyone else runs into this issue: Recreate an account similar to the one that the Apple Store reviewer deleted (with the correct data, permissions, etc.) In the delete account code, check for this account and don't allow it to be deleted. Instead, show a modal that explains that this specific account cannot be deleted, and if they would like to test account deletion, they can log out and create a brand new account to delete. Include this info in the review notes. This way, the onus is on them to create new accounts if they need them, they can still test account deletion, and the reviewer account will be preserved. Hopefully, they will accept this approach. This definitely doesn't solve anything for apps where you are required to go through some sort of buyflow to even create an account though. I'll be interested to hear what people come up with when June 30 rolls around.

Here is the exact reason given for the rejection: We discovered one or more bugs in your app. Specifically, when attempting to login using the email address provided an error appears on the screen. Seeing an error on the screen in this case is expected because in a previous review, they deleted the account we provided them with. Now they cannot log in with that account anymore. Yes, we have already confirmed they have deleted the account. We did not explain to them not to delete their account, but maybe this is what we need to do to prevent them from testing this part of the app? Since there is not much documentation on how 5.1.1 is supposed to be tested by Apple reviewers, I don't really understand what we're expected to provide them (new credentials every time we submit in case they test to delete?). I'm just not really sure how other developers will be solving this problem. It seems like everyone will be in the same boat as soon as they add this functionality to their app by June 30. When we asked them what we should do and explained exactly what I explained above in my first post, we received a canned response with links to developer docs and this forum.