Yeah, not sure if this is related to W10 or not but mine stays awake - or rather does not go into full standby mode. Monitors sleep.
powercfg /lastwake points to harddiskvolume2 and svchost which is not that helpful. OS is on SSD (volume 1).
powercfg /energy points to several things, including two instances of: \Device\HarddiskVolume2\Windows\System32\GWX\GWXConfigManager.exe and for the first instance, it says, "The program has made a request to prevent the system from automatically entering sleep." So this is why I ask about the W10 icon.
The report also points to several USB devices (keyboard, mouse, hubs and UPS), but those are not new and have not had any recent changes made to them in terms of drivers or settings.
That said, for each of the USB devices, the report says, "USB Suspend:USB Device not Entering Selective Suspend". However, then it says, "Note that this issue will not prevent the system from sleeping." For this reason, I don't believe it hardware related.