In Specification Generator, after loading Catalog if you add Section name and try to Add class name, it comes Empty. There will no Class Name Listed inside Dialogue.
This has happened because of Using Plant Design Work-group (PDW) Data option to be checked on in Specification generator. See below image:
Ideally, if we are using OpenPlant Spec this PDW Setting and Use PDW Data should be checked off. Otherwise EC_ CLASS_NAME Field will not get read by Specification Generator.
After Turning this Checked off, All EC_ CLASS_NAME field will come back again.
Now verify result by opening Catalog and adding Section name and Class name. See below: