If I start up a web server exactly how they do it in the BlinkyWebServer example, everything appears to work correctly while debugging (no errors), but I can't access the url on the port. I just get a timeout. I'm using the 14295 build of Windows IoT with a Raspberry Pi 3.
As of build 14295 Windows IoT added an internal firewall. To open up a port:
Open up the firewall with:
netsh advfirewall firewall add rule name=[Any name to identify rule] dir=in action=allow protocol=TCP localport=[Port number]