Office365Tenant.GetExternalUsersForSite() method is returning "Unknown Error"

Hi,

We are using "Microsoft.Online.SharePoint.TenantManagement" namespace in our program. The Office365Tenant class has one method GetExternalUsersForSite()  which retrieves all external users that have access to particular externally shared site.

We have two externally shared sites in our SharePoint Online.

https://abc.sharepoint.com/sites/EXT1 and 

https://abc.sharepoint.com/sites/EXT2

Using the method GetExternalUsersForSite() we are able to fetch all the external users for site EXT1. But it is throwing an "Unknown Error" for site EXT2.

This is strange, as both the site belongs to same tenant and does not have any difference as far as external sharing settings is concerned.

Kindly suggest.

Best Regards,

Kundal