So, the overview for recent apps tends to not show me anything in the last few days... I use the phone a bit, and nothing there anymore. A restart solves the problem, but after some time... Boom... Does not show any recent app.
I'm also experiencing this on my Xperia X constantly, and restarting the phone will do for a while as @2literpopcorn said above but it keeps happening. No killer app or Antivirus or managing app installed.
I do not know how to start Safe Mode. But it behaves just my phone also. I have the bug only recently, just like Pokemon Go. Can it be that this game causes this bug?
I have the same problem. Phone was factory reset a few days ago, no task killers installed. I press the overview button and all I get is the small apps at the bottom and a message saying,"no recent apps". I restart the phone and it works properly. But at some stage during the day it will stop working again (maybe after using Google voice recognition. Not sure) and I have to restart again. Didn't do this on lollipop!