OS X has a feature where when you hold down a key like h,j,k,l, it brings up a menu with diacritics for that letter. This intercepts keyboard events when you are trying to use Vim in a Citrix virtual desktop session. The symptom is that your Citrix will beep at you whenever you hold a key down.
The fix is to disable this popup menu using the command:
defaults write -g ApplePressAndHoldEnabled -bool false
This setting won't take effect until you log out and back in to OS X.
OS X updated and broke everything like usual: xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
Run xcode-select --install to fix.