Log into your GateKeeper admin consol using your GateKepeer Hub URL.

From the Events dropdown list, select "GateKeeper Lock."

Groups
Select Groups
Computers
Select computers
Users
Select Users
Events
GateKeeper Lock

Type or choose a user from the dropdown list.

Under the Events column, hover your mouse icon over GateKeeper Lock, and the software will display the type of lock event: Proximity, Button, Timeout, or Inactivity. 

How to see why GateKeeper locked the computer.