When creating a form with drop down selection fields, the first one is populated with static values. The second one is populated using a SQL query that includes the value selected in the first drop down field. So, the contents of the second list will be different depending on the value selected in the first drop down list.
These two fields work as expected if both fields are visible when the form is opened.
However if the second drop down field is hidden until after the selection is made for the first one, the second drop down only shows "Loading" and never gets populated with the expected values.
Service Catalog 17.4 and above
A hot fix was provided to resolve this problem. Final fix will be included in RU4.
The problem was first encountered with Service Catalog 17.4 RU2 but could possibly be found with other versions as well.