Fix: Fedora 25 Server stuck at “Setting up installation source”
Installation started, everything selected and you end up with the following screen and ongoing process of “Setting up installation source”.
Possible problem, that can cause this is related to the networking (or the lack of decent connection in this case). Probably caused by Bug 1048344, more info on which can be found here.
So after removing the virtual switch, everything continued flawlessly 😊.