My client said that they are having issues with Outlook 365 via the local Outlook app when Fiddler is also open/running.
The client goes to open outlook and it just sits and spins and never opens. But as soon as she closed out of Fiddler, she was able to open email no problem. They have even had to reboot their computer in order to open Outlook.
See attached for how I have their settings set up.