@David_Fox: Have you tried uninstalling Insync, removing the /usr/lib/insync folder, then reinstalling Insync?
Running Fedora 25 here and had problems updating insync.
Just uninstalled insync1.3.14 (dnf remove insync) , deleted /usr/lib/insync (rm -Rf /usr/lib/insync) and reinstalled insync successfully (dnf install insync).
All fine now.
Following @lpugoy instructions fixed the issue for me. I was stuck to f21 package, looks like its been broken for a while.