There is an issue with permissions and iohub in OSX, or more accurately an issue with OSX in how it handles permissions. You can override it, but I’ve had somewhat mixed results and it looks like you need to re-enable it every time you update psychopy. (Windows and Linux do not have this issue.)
In your system preferences, go to ‘security and privacy’ and then to the ‘privacy’ tab, and in the list on the left choose ‘accessibility’. Drag psychopy into the list of programs from your apps folder, and check it. It should then allow iohub to start up.