Problem with AD User Import Sharepoint 2019

Hello everyone,

we have recently finished a migration from SharePoint 2013 to SharePoint 2019. I've run into a problem with the sync of user via AD import. Configured are two sync connections to different domains. These domains are in a federated trust. The sync runs but no users will be added from the external domain called B. From Domain A(our own domain in which the sharepoint farm resides) all existing users were added but no new User will be added.

I've found the following in the SharePoint-Logfiles for both domains:

ProfileAttributeSyncJob:ProcessMapping -- No tenants to sync from DC 'domain.site-city.xy' at RootOU 'DC=DOMAIN,DC=ORG,DC=XY', continuing to next DC

I've alread checked the permissions on the app, on the profile used for querying the dcs to no avail.

The domain gets populated after connecting with corresponding user for each domain and I can see the OUs and users of the domains.

With kind regards,

M. Miller