Another update, the receiving issue is solved, yet I'm unable to move the accounts to online.
And just noticed, if I start the migration process from the "Office 365" tab in our ECP, there are certain accounts that are NOT listed for selection. Those particular accounts are not migrating to Office 365 I select any of it from the on-premises ECP and do the migration process. And the result is as shown above in my last update "Error: MigrationPermanentException: An error occurred while processing this item."
Nice, huh? :)