fedora 26 now has mp3 support. so that's where the conflict arose. the GUI upgrade through GNOME Software? try checking for updates again and you may be offered it again. Anyhow, please do remove the sox package before attempting the upgrade again either via the GUI or terminal.
I'm not sure it is a bug but it is certainly a valid feature request. You send both via https://bugzilla.redhat.com
You'll need to register a free account to use it. Check for an existing request first though using the search function on that site.