If you do not want to read the whole story then here is the issue;
Implicit Managed Properties are CASE-SENSITIVE. Make sure you copy and paste the property name in your code. I was using it in Search's REST api and it was not working because I used "deptOWSCHCS" instead of "DeptOWSCHCS" (notice the first letter).
What is Implicit Managed Property?
SharePoint automatically creates a managed property...