"tried couple of troubleshooting provided on public arctile but didn't helped."
Such as?
Have you tried?
Adding the mailbox then removing?
Add-MailboxPermission -Identity "Jeroen Cool" -User "Mark Steele" -AccessRights FullAccess -InheritanceType All -AutoMapping $false
then:
Remove-mailboxpermission
Remove-MailboxPermission -Identity Test1 -User Test2 -AccessRights FullAccess -InheritanceType All
Also try this switch:
-ClearAutoMapping
This parameter is available only in the cloud-based service.
The ClearAutoMapping switch specifies that the mailbox is automatically mapped (auto-mapped) by Autodiscover only into the mailbox owner's Outlook profile. The mailbox isn't auto-mapped to other users who have FullAccess permission to the mailbox.