Monitor won't sleep in Windows 10

I am trying to set my monitor to sleep after 5 minutes to save electricity and also not have to do it manually and have found that something is stopping it. I have an Acer Aspire V5-571G laptop with a Samsung 27" C27F591FDE monitor.

I have tried a number of things after researching this common problem on the internet and they all fail to fix the issue. During testing I have seen the monitor go into sleep mode a few times out of about 30-40 tests. This seems more random anomalies and there is no consistency in the conditions or state of the PC when it does work.
1. I have tried the powercfg commands to see if there is anything interrupting it - NONE.
2. Removed all USB devices.
3. Done a Windows "Clean Boot".
4. Installed a fresh copy of Windows 10 without any other software or drivers.
5. Booted into Safe Mode.
6. Disabled or uninstalled Video card drivers.
7. I set the power button in advanced power settings to turn off the monitor. It works but then turns itself back on within 5 to 10 seconds. Something is waking it up.
8. Disconnecting internet.
9. I've installed third party software to utilise keyboard shortcuts to switch off the monitor manually. They either don't work or again, it switches itself back on within a few seconds.
10. In the Event Viewer, the only interesting entry is Event ID:34 BTHUSB - "The local adapter does not support an important Low Energy controller state to support peripheral mode. The minimum required supported state mask is 0x491f7fffff, got 0x1fffffff. Low Energy peripheral role functionality will not be available."
I am not sure if this has anything to do with it but it's recurrence does not match every attempted sleep test.

Since this isn't even working in Safe Mode, either a very basic windows process or service is kicking it into life, or my laptop hardware is responsible. I can't confirm absolutely if the monitor sleep function has worked in the past with previous versions of Windows either.

I'm at my wit's end with this so any *USEFUL* more detailed technical fault finding or diagnostic tools or ideas would be greatly appreciated.

See the advanced Power Options. Go to Sleep->Allow Wake Timers and change it to disable. Go to Display->Turn Off Display and set 5 minutes (or whatever you like). If these don't work, right-click on your Desktop, select Personalize and then select Lock Screen. Scroll down and click on Screensaver settings. Select Blank, set the desired duration in minutes and then OK. This should at least give you a black screen.