In Microsoft Exchange Server 2019 or Exchange Server 2016, if an error occurs in a move request or you cancel the move request before the move is complete, the mailbox can't be deleted from the destination database. After the retention period that you defined by using Set-MailboxDatabase cmdlet has already passed, you can still see it in Get-MailboxStatistics cmdlet's result. This issue may consume lots of disk space in Exchange Server.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.