Thanks for posting your question in the Microsoft Q&A forum.
It seems that everything is Ok, just Azure AD password write-back not working.
Please consider these step:
1- Ensure that your Azure AD Connect is configured for password write-back(Enabled). You can verify this by opening the Azure AD Connect configuration and check the password write-back settings.
2- Make sure the account used by Azure AD Connect has the "Reset Password" permission in Azure AD.
note: you can check the event logs on your Azure AD Connect server for any errors or warnings related to password write-back. I'm sure you can find valuable information about what might be going wrong.
Best,
** Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful **