Windows waking from Sleep/Hibernation after 15-25 minutes

Question

My machine is waking every 15-25 minutes after they are put into sleep/hibernation (issue persists with both). I'm running Windows 10 right now, but the issue was already present in Windows 8.1 (and hence I upgraded, hoping to fix the issue).

I know it is not the first time this issue has surfaced. But after looking for a solution for multiple hours, no solution came up. Here's what I tried so far:

1. Turn off "Allow this device to wake the computer"

I've turned off this option for every single device in the device manager. powercfg -devicequery wake_armed returns NONE.

Lastwake doesn't yield anything useful either.

2. Disabled wake timers

Also, Multimedia settings -> When sharing media -> Allow the computer to sleep.

3. Don't allow automatic maintenance to wake up PC

4. Power-Troubleshooter: All Wake Sources unknown

This is especially frustrating. Every single entry shows an unknown wake source.

5. BIOS: Disable Wake

My motherboard is a MSI Z87-G43 (unfortunately I can't take a screenshot of the BIOS).

6. Task-Scheduler: No tasks waking the PC

7. Remove Ethernet cable

I've unplugged the Ethernet cable before going to sleep/hibernation. No effect.

8. Energy report

No devices have "made a request to prevent the system from automatically entering sleep."

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Does anyone know how to fix the issue?