I haven’t experienced this problem, but I know of people who have. They’ll put their laptop into suspend or standby mode, and after a few seconds, the laptop will spontaneously wake itself up. Someone gave me this tip that might (might) help you figure out what is wrong.
Open a command prompt and run the command
powercfg -devicequery wake_from_any
This lists all the hardware devices that are capable of waking up the computer from standby. But the operating system typically ignores most of them. To see the ones that are not being ignored, run the command
powercfg -devicequery wake_armed
This second list is typically much shorter. On my computer, it listed just the keyboard, the mouse, and the modem. (The modem? I never use that thing!)
You can disable each of these devices one by one until you find the one that is waking up the computer.
powercfg -devicedisablewake “device name”
(How is this different from unchecking Allow this device to wake the computer from the device properties in Device Manager? Beats me.)
Once you find the one that is causing problems, you can re-enable the others.
powercfg -deviceenablewake “device name”
I would start by disabling wake-up for the keyboard and mouse. Maybe the optical mouse is detecting tiny vibrations in your room. Or the device might simply be “chatty”, generating activity even though you aren’t touching it.
This may not solve your problem, but at least’s something you can try. I’ve never actually tried it myself, so who knows whether it works.
Exercise: Count how many disclaimers there are in this article, and predict how many people will ignore them.