The same data source has been added to more than one hold in a case in O365.
Please follow the below steps to remove the data sources manually from the O365 Compliance Center.
1. Login to https://compliance.microsoft.com/classicediscovery
2. Click on the Case under which you want to remove the Mailbox/OneDrive Location from the Hold.
3. Click on the Hold tab.
4. Click on the Hold from which you would like to release OneDrive and Exchange Online data sources.
5. Click on the Edit icon in the hold screen.
6. Click on Next Button.
7. Under the Choose Locations section you will be able to find the Exchange mailboxes and Sharepoint locations category. Click on Choose users,Groups or teams.
8. Uncheck the exchange online mailboxes in the Exchange online mailbox section and Click on Done.
9. Click on Choose sites hyperlink.
10. Uncheck all the sites in the hold and click on Done.
11. Click on Next.
12. Click on Next again.
13. Click on Submit.
14. Once you receive the Succeeded message please click on Done.
15. Click on the Hold again to make sure that the Mailbox & Sitecount as Zero.