Starting yesterday, we noticed our newly-imaged Macs have fast user switching disabled when a standard user signs in and the setting remains grayed out even when the Users & Groups menu gets unlocked by an admin.
JAMF has uncovered this symptom in 9.93, tracking the issue as PI-002764. It occurs when a Configuration Profile with the Security and Privacy payload is pushed out to a machine, regardless of what the profile is setting on the machine - it will disable fast user switching. Per JAMF, the only workaround to the issue is to completely log out of the computer as one user when switching to another.
Hey @badibalt are you pushing out Managed Preferences (MCX) and Configuration Profiles from the JSS? Do you happen to push out System Profiles and User Profiles? Did your User Profiles used to have the Login Window payload?
EDIT: Grab a test system and exclude it from all ConfigProfiles and MCX, then slowly start adding profiles back. I found a User Profile that was the culprit in my environment. Read here for some direction: https://macmule.com/2016/05/09/icloud-spotlight-login-window-issues-with-jss-9-9-the-security-privac... if you can download the profile and see what it is actually applying it might help.