I had the same problem with my Windows 10 desktop machine last year. I spent ages trying to diagnose it, gave up in the end and ignored it. It fixed itself a few months later.
There are commandline tools in Windows to show why it isn't sleeping, though in the end they didn't help me fix the problem.
https://docs.microsoft.com/en-us/windows...ndby-sleepstudyhttps://docs.microsoft.com/en-us/windows...nd-line-options
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Remind me to change my signature to something more interesting someday