FWIW, after letting the window site idle for a couple of hours, I found CPU utilization to be near 0. I don't know really how long. That and JS profiling shows nothing leads me to believe it's some background task that eventually finishes or times out.
This also happens to me on Win 10 build 1607, but only when I install hyper-tabs-enhanced. As soon as I remove it, CPU usage goes back to normal. Curiously, the Desktop Window Manager also cranks up at the same time.