I'm not sure what "Win 8.1 phone" is. Is Fiddler running directly on your tablet, or on another PC?
When you are testing your metro app, are you doing so from Visual Studio or are you running it directly? When you are running it from Visual Studio, it should automatically get an AppContainer Loopback exemption; when you are running it standalone, you need to manually use the Win8 config tool.
If you are using Visual Studio, what is the callstack if you break while it the app is in "perpetual load"?
When you installed Fiddler's Trusted Root certificate, did you accept the prompt to trust the certificate "Machine-wide" and not just inside your user-account? Using the Machine store is necessary to debug Metro apps.
What is the URL that your app is trying to access? Do you see *anything* coming from the app in Fiddler? If you use other Metro apps (e.g. the News app, etc), can you successfully see their traffic inside Fiddler?
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