In the latest r20.2.2 based Release Notes there is a section documenting OpenAPI OData changes.
It refers to the disassociation between the interfaces and qosclassmaps endpoints with the $expand= options for qosclassmaps and qosreds. It states:
If we're using the $expand=qosclassmaps or $expand= qosreds options in existing scripted queries, will they work if using different endpoints?
Performance Management r2.8 and newer releases.
The change documented began with the r2.8 release.
The suggested alternative endpoint is the specific metric family the data is sought from.
Most often that would be http://<DA_HOST>:8581/odata/api/qosclassmapmfs.
Use of the odata/api/interfaces or odata/api/qosclassmaps are the only ones that won't work with the referenced expand values.