Interesting. Do you see Err on E30 screen? Maybe other input connected?
Yes, the E30 display does flash "Err", just before it goes to sleep. No, there are no other inputs connected.
A second way to get the E30 to sleep is to switch the input from USB to one of the other interfaces. It then also flashes "Err" before going to sleep.
Also if you unplug the USB cable, does it standby?
Yes, that's a third way ...