I’ve helped many users who say Fiddler has “fixed” their issue. Unfortunately, this is a bit deceptive. Fiddler is an excellent debugging tool for web apps, but it does not permanently resolve problems. What it does do is act as a proxy with its own connection settings. This allows it to act as a “man in the middle” and even decrypt the traffic to provide better more insight into application behavior.
While the general rule of thumb is to capture at the client, or at least start there, sometimes it’s necessary to take captures at both ends of a connection. The client perspective will allow you to view the problem as it is seen from the client. The server perspective might show the same thing. Or, in some cases like this one, it will provide the reason for the problem. The problem was that a webpage wouldn’t load.