Typically, USB hubs are a problem, but the easiest way to find out is to start by unplugging the hub - if problem solved, plug it back in and start removing individual devices from the hub to see if you can narrow it down. If you identify the device, try swapping its USB cable with another to see if the cable is the problem. If not, try plugging that device directly into the USB ports on the Mac to see if that solves the problem.
Repeat for all other devices if it doesn't turn out to be the hub or something attached to it.