While shut down or restart getting message that "someone is still using" my pc

Nearly all options examined, we may have come around full-circle with this issue. The issue of restart after shutdown, or unable to remain in S3 sleep mode, may inherently lie in the individual computer's BIOS handling of the S3 sleep mode. S3 sleep mode energy expenditures can be somewhat adjusted through the Power Options in system, such has USB charging capabilities on-off, and a few other minor adjustments. Requirements such as keeping charging capability for USB, etc. might be examined, and also power-down of NIC adaptors, another adjustment built into the NIC adaptor driver structure, not necessarily in Power Options. I have found that nearly ALL NIC manufactures allow for power-off states in S3, but allow for default power for "Wake On-Lan" settings, which seems to be the default setting! I always uncheck these power boxes for WOL. After this, one could examine the Task Scheduler for any remaining tasks that may be restarting the machine after it enters the S3 sleep mode. What was the Event just before the machine restarted, or what woke the machine at 3am in the morning, bathing your room with blue-white light? A neutrino surge that interacted with some processor gates? As stated in the beginning, a tough-nut to crack may just be the computers firmware handling of the BIOS S3 sleep mode, which most S3 BIOS settings have not evolved beyond the standard "Auto" setting.

I agree it is like using a sledgehammer to crack a nut, however I tried it and it made no difference. MS technical support were unable to fix this and the only suggestion that seemed to work was to disable fast user switching which sadly prevented anyone else from logging on, so that was no use.

I not you say this is no big deal, but I find that having thought I switched the PC off, I find that its still on in the morning, having burned unnecessary, electricity. There are two regular users and a 3rd non regular user and this issue is very frustrating and it appears Microsoft has no idea how to fix it. I also note that there are other builds of Windows (8 and 7) who have reported the same issue when I surf for an answer. Surely it is not beyond the MS technical people to solve this as it has been going on for quite a while.

Thankyou PreciousLeb for your reply.

I'm not disappointed. (Whatever made you think I was? Anyway.)

I was simply reporting that, like Mon.k11, I was seeing something that looked incorrect to me, with some details of the circumstances, in case anyone in Microsoft wished to investigate it further.

I did say that it was no big deal for us, and it isn't. If you think the problem is local to our situation, not widespread, and not worth following up, that's ok, that's your choice. The Fall Creators Update is otherwise working well for us so far as I can tell, I am relieved to say.

Thankyou for your suggestion about rolling back to the previous version, but really that would be a sledgehammer to crack a nut. I haven't got the time to spend messing about like that, and as this machine is the only one we have, the less risk we take with it, the better. We always know which of us is signed in and who isn't, and if we simply have to click "Shut down anyway" when necessary, we'll just do that.

Best wishes,  Terry

You fix this by changing the Privacy settings in the Accounts section.  

Go to Settings --> Accounts-->Sign-in Options

Scroll down to the Privacy section and turn off the option that says  "Use my sign-in to auto finish setting up my device ....reopen my apps ...etc

You need to do this for each user profile on the computer.  After this change, I have not seen that message again.

After getting the notification in question,  the message popped up for the first time this morning. 

Reading this thread it would appear that concise information is scant, even from Microsoft.

As an end user who knows very little about sorting out problems on a PC, I find the whole issue disturbing to say the least.

I'll work backwards, time wise through these suggestions to see if I can resolve my problem....

Newest installation variables for Win 10 allows for you to setup using either a Local, or Roaming account. Since my installation is not on a Domain, I have setup Win 10 with a Local account. I don't see any advantages by using a Roaming account, therefore, I sign-in to my MS account with a Local account, and this solved many problems I experienced, including resume from S3 sleep, where the machine could not find its current operational settings via Device Census. All seems to be good for now.