Ad connect - duplicate smtp proxy addresses sync issue

[Max_Power]

We have an hybrid Exchange setup at the moment.
A mailbox was mistakenly given a wrong alias already attached to another mailbox.

Thus, we had a syncronization error displayed on the admin center saying :"We detected a duplicate Proxy address conflict on the value . All attribute values need to be unique across objects. To resolve this conflict, first determine which object should be using the conflicting value. Then, update or remove the conflicting value from the other object(s). This error was detected on ."

When we cliked on the error details we could see the two mailboxes ( the correct one and the wrong one) displaying the duplicated alias.
So we removed the alias from the wrong mailbox on the exchange Online but the error was still showing up because the wrong alias was still attached to the mailbox on the "local Exchange Console".
So we removed the alias on the "local Exchange Console".
Now the we have one remaining error refering only with the correct mailbox. The wrong mailbox is not showing up anymore on AD sync error details .
I've checked all the AD objects either on Ad or Exchange or O365 and everything should be all good but still we have this error.
Is this an expected behavior or do I have to do something or wait before the error disappear ?

[#2]

Should I consider this topic as an answer to my question :
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_o365admin-mso_other-mso_o365b/how-to-cle...

I hope not ...

[#3]

I've had duplicates before, but they usually will just clear themselves as long as you removed the duplicate on the on-prem side of the fence. But it's usually on the next sync. You might try preforming a start-adsyncsynccycle -policytype initial to do a full sync, that might clear it up instead of relying on the delta.

[#4]

Where are you seeing the error currently? If it's only in the O365 Admin Center, you can ignore it - it's known to show outdated info. If you are seeing it in the MIIS Client or in the email notifications you are receiving for sync, then you have to double-check the attributes.