is your ConfD CDB up & running when you try to run the subscribing application?
debug message seems to point directly to problem - do you have “WMGEBuilder” container/list/leaf in your CDB root to be subscribed to?
If so, how is the “WMGEBuilder” defined in the YANG model? Do you have some callpoints attached to this “node” - e.g. transformation/data provider etc.?