I upgraded Fiddler to the latest version (v188.8.131.52) and for some reason it is no longer capturing iOS traffic. I have not actually tried this for many months so admittedly the problem may be unrelated to the upgrade.
I have done this many times in the past where I set the HTTP Proxy on my device to the IP of the machine running Fiddler and it instantly captures all the traffic.
I verified all the settings and everything seems fine. In fact, when I visit http://myip:8888 from my device I successfully receive the Fiddler Echo Service. However no traffic is being captured.
My setup is a laptop and iphone both on the same non-corporate wifi network.