Command + C does not always work on first try on MacOS

Command + C does not always work on first try on any of my four Macs. I often highlight text, press Command + C, head to another window, press Command + V only to find that the original text did not copy.

I recently installed a fresh copy of macOS High Sierra and I continue to run into this issue, particularly in RStudio.^* The issue never occurs on my PCs.

Do others have this issue? How can I resolve this?

^*I use bettersnaptool and enable three finger dragging, but the issue still appears when I disable them.

I think it's possible for Apple's Continuity Universal Clipboard feature to cause something like this, depending on the quality of the signal connection with any nearby iOS devices.

Perhaps try turning off "Allow Handoff between this Mac and your iCloud devices" in System Preferences > General and see if that helps.

I've found a cause of the same problem. An app may use it as a hotkey. In my case, I use a dictionary app (Eudic), which will read the clipboard if cmd+c is pressed twice.

An easy way to check whether it is caused by an app is to activate the Guest account, which usually has few autostart apps, and to check whether the problem still exists.