How are you using Fiddler to test your URLs - using the Composer or just by starting it and letting it work while navigating to the URLs?
502 means "Bad gateway". Are you using proxy in order to access those URLs? If yes, you can set Fiddler's proxy from the options menu.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items