Wait for the Microsoft throttling to end. Then the task ought to continue to make progress.
Please have a look at this migration tips guide to ensure you are doing what you can to minimize the throttling being imposed by Microsoft:
https://support.quest.com/on-demand-migration/kb/328509/odm-migration-strategy-and-best-practices
In addition, the On Demand Migration Strategy and Best Practices for Migrating Active Directory, Mail, OneDrive, SharePoint Online, and Teams’ Content can be found here:
