Step 1) Go into app settings
Step 2)click on App Lock
Step 3)Clear the apps cache(here App Lock’s cache) and force close it
Step 4)Go to Whatsapp(or any app ) which was locked, it will be unlocked now
Step 5)If you were snooping about, then just open and shut App Lock, the apps will get locked again and no trace of app being opened will be left.