Restoring ANY database to Azure MI fails
Just got feedback from Microsoft, this is a known issue which is currently being fixed. 

As per their recommendation creating the backups with the option CHECKSUM leads to restorable backups.

BACKUP DATABASE [DBNAME] TO URL = N'https://&lt;storage_account&gt;.blob.core.windows.net/&lt;backup_container&gt;/on_prem_db_full.bak'
WITH CHECKSUM