I also have problem in traffic monitor UI (maybe since 376.45) and no matter reset of history files can correct it. "Global" shows the traffic graph properly but once click on one of the 3 "Per device" elements drop down box, the UI missed the devices info section entirely.
(on IE11, Chrome, Slimjet and ios Safari).
Works for me. Make sure you don't have a device with a non-standard name (for example with a quote in its name) on your DHCP reservation page or on the Network Map.