You're in luck because Fedora 25 hits "end of life" in a few weeks. So you can start over with the current Fedora 27, maybe that will solve the problem?
If you want to stick with Fedora 25, first of all, did you know you can switch back from Cinnamon from KDE at the login screen? (The exact method will depend on the display manager in use.)
Second, did you know that the package manager logs all of its transactions? So, by looking back at the history, you can see exactly when Cinnamon was installed, and why. Perhaps it was brought in as a dependency of a package you chose to install? Check /var/log/dnf.log or use the 'dnf history' command.
