usually a search using objects or search will return any objects that have values for that attribute.
if you search for any value in the UI, does it work as expected?
when i search for the values of the reference Attriutes in the UI the correct objects are displayed. But searching using REST-API with the ID doesn't seem to work. I'm not sure if REST API search is working the same for reference Attributes like for Custom Attributes.
Search in REST-API for custom Attributes is working but not for reference Attributes.
I recognized that the ID should have the ending <ID>_derived. Then it works!