1.5 Ensure 'Power button instantly locks' is set to Enabled
Information
Pressing the power button should lock the device instantly. Rationale: Pressing the power button instantly puts the phone to sleep. Enabling Power button instantly locks setting ensures that the device is instantly locked as well.
Solution
From the MobileIron console, open the Policies & Configs -> Policies view. Under the Security Policy verify that Grace Period for Device Lock is Immediately.