This is discussed in docs:
https://www.servicenow.com/docs/bundle/xanadu-servicenow-platform/page/product/configuration-managem...
where the tasks are assigned to the "System Administrator" user when the "Managed by Group" attribute is empty for the CI.
Since we do not use that field yet, and are only directing these tasks to the core team responsible for managing the CMDB at the moment, our current solution is an after insert business rule on the "cmdb_data_management_task" table that sets Assigned to/Assignment group to what we want.
-on Xanadu release
