When trying to download the manifest package generated after using the Insane Mode, Sharegate displays the following error:
Unable to download the Manifest package: you are no longer linked to a Microsoft Azure storage account.
The manifest package contains the metadata that Office 365 will use in order to import the list items and documents. It also contains log files generated by the import job. Those files are located in the Azure Storage account provided in Sharegate's settings.
This error happens when the Microsoft Azure storage account was unlinked in the settings.
Simply reconnect to your Microsoft Azure storage account and try downloading the manifest package again.