Unfortunately I'm experiencing same problems. We have 7 Sticks used as kiosks showing web page and we're experiencing random sleep mode.
All power settings set to off, connected to different versions of screens (LG, Samsung, etc) and sleep mode triggers at random. It works for 3-4 days and next day we find it in sleep mode. This is extremely annoying.
And the fact your question here is not replied for 4 days now is even more annoying.
It appears to be related to the system or drivers (power management) as it affect only sticks showing web page in browser. Sticks showing PowerPoint presentation using PowerPoint Player seems to be working fine.
I am using the ICS (running Ubuntu) as Digital Signages. So far, they seem to be working fine even after running for 3-4 days. As I am not running Windows but Ubuntu, my experience could be different from yours. If different OS behaves differently, the issue should be software related and not hardware, which is constant with what HaraldB is saying.
I found that the bios has a hidden gem in it, you can change the device profile for performance and then clean up the OS so that it too is set for performance and all of the bugginess goes away. Windows 10 seems very stable on the device and seems to better maintain a wifi connection. I also changed the windows update setting to download and wait for approval, this keeps the windows updates from crashing the OS.
Do you mean that by setting the device profile for performance, you found that it is more "stable"? If so, that is pretty good news
I don't know if this is of any help but WeK05 suggests that to permanently disable the system from sleeping, connected standby has to be disabled in the registry. Open regedit.exe, go to HKLM\System\CurrentControlSet\Control\Power\ and change the value for the key CsEnabled from 1 to 0.