That is something that was in the back of my mind. But even on a 15 amp circuit, I can't see that number of devices overloading the circuit. A defective power strip is certainly another potential thing that could be checked. Many power strips today have current monitoring circuits with surge protection, and a failure there might show up as a power shut down that might appear to be operating normally when you turn everything back on.
If the Roku is showing the boot screen when you turn everything back on, that would indicate a loss of power, not just a simple power down that the power button would trigger. The Roku is never "off", just goes to sleep. So if you see the Roku bouncing logo when you turn the TV back on, the Roku lost power. And there's no way the Roku could have done that.