I think this problem is facing by who installed KDE Connect on their system. I have Ubuntu 16.04 and I was also facing same problem with nautilus-3.20.3 while ctrl+c or right-click => copy. I analyzed system monitor, /var/log/syslog and found that when we press ctrl+c, a process name 'kdeconnect-cli' appear in system monitor.
So I renamed this file like '__kdeconnect-cli' in the directory /usr/bin and the problem solved but now I am not able to send files to my Android device with right-click.
'kdeconnect-cli' is a KDE Connect CLI tool that is responsible for sending files with right-click to your Android device using KDE Connect tool, I guess.
Now you have to use kdeconnect-indicator icon in your status bar to send files to your Android.