TooManyBadItemsPermanentException error when migrating to Exchange Online?

Nice article. However, unfortunately it is not the case that only the objects synchronized from AADConnect appear in ExO. Permissions granted over objects like Domain Admins, Account Operators, etc. (if present on the source mailbox, having explicitly granted permissions), are also happily transferred to ExO, being mapped to the respective tenant Domain Admins, Account Operators, in quite a bizarre way (map from a group which is not synced from on-prem to a group that the O365 customer has no control over).