[ks002]

Unfortunately this seems to be a problem with many windows devices and I have it as well from time to time. I also have the impression that once solved , the problem might reappear with a new windows or dirver update. I just had such a situation a few weeks back and it was driving me mad! I changed several settings , including swithing off 'fast startup' but honestly I cant say the one setting that did the job. You may also try some debugging described here:
https://www.gfisk.com/computer-wont-stay-in-sleep-mode/

Also I noticed that the not sleeping pc problem is more likely to appear when you quickly unconnect it from the power supply and close the lid basically at the same time ('leaving office')
good luck!