We have the same issue, in the unit-tests of a swift-package. In our case, moving the tests to a test target under the sample app didn't help. FB8885728.

In another thread, PBK said the sandbox user never gets an email: https://developer.apple.com/forums/thread/72083?answerId=215874022#215874022 If that's true, there's no need to use an address that you can receive email at.