Was on the phone today when my call suddenly stopped and the “recently used” screen went blank. I’ve turned off and taken out battery etc but on switch on that screen is still blank.
The recently used apps list is a widget so your apps will still be there, just have to go to All Apps to access them again.
On the recently used apps widget there is a button to “Reset” which clears the history associated with your app usage. It wouldn’t be unheard of that this could have accidentally been pushed. Any chance this is what’s happened?