Sometimes the serial buffer starts choking and getting slow on the USB side of things. We had a couple other posts about that. This is because from the JeVois side, we have no way of detecting whether someone is listening to the serial-over-USB on the host or not.
So, if you had serial outputs also sent to USB, try to disable that. In your initscript, you should use
setpar serout Hard
Other than that, it may be some issues with your arduino. You connected the red wire from JeVois to the correct voltage on your Arduino, right?