Windows 10 Fast User Switching doesn't work on some machines

[Filip Matijević]

Hello,

I have as strange one here with Fast User Switching (FUS)- so ideas are very welcome:

• I have a number of domain joined PCs all running up to date Win 10 Pro
• some of them simply don't have Switch User option on the Lock Screen
• they have Switch User option in Start Menu, but using it causes current user to be logged off before returning to Logon screen
• I've played with the usual suspects (Registry, Group Policy, Local Policy...) that control the behavior of FUS - w/o any effect
• chkdsk, sfc, dism found no problems and even repair install didn't help
• attempting to troubleshoot the issue I've made a drive image from one of the machines and when run on Hyper-V, VirtualBox or another physical machine the Switch User is there and working as expected (!)
• moving the imaged disk back to the problematic machine and the problem reappears
• this indicates that HW has something to do with it - by looking a the affected machines they seem to be older HP machines (dc5850, 6005 Pro) - all non UEFI with TPM 1.2 chips on board and otherwise quite different (Intel and AMD based).
• they are all running their latest BIOS and disabling TPM in BIOS doesn't make any difference - I can't imagine that any of other device might have any effect on FUS in Win10
• I see nothing EventLog that might indicate the problem and even running ProcessMonitor doesn't indicate anything obvious
• currently I'm pondering if some driver/service can have a role in affecting the Win10 behavior (possibly including BIOS settings) - so that this essentially becomes HW dependent issue
• on affected machines it is possible to have another user signed in by locking the current session and logging in as another user from Lock Screen

This has been bugging me for a week and it's driving me insane

Thanks

TL;DR
Fast User Switching (FUS) works depending on whether the drive is being booted on different hardware. I'm looking for any HW (driver/service) that might have an impact on FUS

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