Thank you for providing an update regarding the matter and sharing the solution with the community!
I will investigate more about the expected behaviour of the presented scenario and forward these recommendations to the appropriate team.
I will be marking this reply as a solution in order for the topic to be closed and I will be quote it here:
ROOT CAUSE [SOLVED]:
The conflict was NOT with email or username - it was with the PHONE_NUMBER field!
Auth0’s soft-delete period applies to ALL user fields including phone_number. When a user is deleted, their phone number remains reserved for 24-48 hours and CANNOT be reused, even with completely different email/username combinations.
If you have any other questions or issues in the future, let un know by posting around here again!
Kind Regards,
Nik