eDiscovery search: Sites not available when adding a Group data source

Hi,

I am attempting to use Purview eDiscovery to search a SharePoint site associated with a Group.

When adding the Data Source, I search for the URL of the SharePoint site, and the Group is returned.

However, after selecting the group and clicking Manage, it indicates Sites are "Not Available".

What causes this, and how do fix it?

My user is a member of the "eDiscovery Manager" role group as an "eDiscovery Administrator", and licensed with "Microsoft 365 E3" and "Microsoft Purview Suite". It is also an Owner of the target Group / SP Site.