Hi @LM-5132
Thank you for posting your issue on Microsoft Q&A.
I understand that you are resetting the password using the Self-Service Password Reset (SSPR) feature with a test user's account and you can reuse the same password.
"By design for Microsoft Entra ID, last password can be used when for passwords reset but cannot be used for password changes".
In the document you provided also tells the same that the last password cannot be reused when a user changes their password, but last password can be used for password reset.
Hope this helps. Do let us know if you have any further queries.
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Thanks,
B. Siri Chandana.