Did  you factory reset your device and enter "afw#mobicontrol" when being prompted for Google Play account to get your Soti Android Enterprise device agent installed and enrolled? If not, you are probably in work profile mode, rather than managed-device mode. You can confirm by checking the "Active MDM API" field in the "Device Configuration" tab in your MobiControl device agent.  Also, apps in work-profile mode has a small orange suitcase at the bottom right corner of the app icon. 

I have tried Kiosk mode successfully in tens of device models in managed-device mode, but not in work-profile mode.   I think  Kiosk mode is not supported, nor does it make any sense, for devices in work-profile mode.  If work-profile managed apps can occupy the whole screen in Kiosk mode, a device user cannot activate his/her personal apps not managed by MDM/EMM.