My computer is on Windows 10 Home Build 2004. I just had a similar issue that it wouldn't go into sleep. To check what was causing it, I opened a Command window in Administrator mode and entered
powercfg /requests
The only thing listed having power requests was
[PROCESS] \Device\HarddiskVolume6\Windows\System32\MoUsoCoreWorker.exe
USO Worker
A quick search on Google showed me MoUsoCoreWorker.exe is related to Windows Update, so I opened the Service Manager and restarted Windows Update service. I checked again with powercfg, and nothing was listed. My computer has been able to go to sleep.
I am not sure whether this issue is completely gone. But at least a quick restart of Windows Update service makes it go away.