app switcher not working in ios 9
I have an iphone 6s running ios 9.3.2 and noticed recently that the app switcher screen doesn't have any icons (when I hold on left and swipe right) so I need to double-click the home button to see all open apps. Can anyone help me figure out how to fix this? I've already turned my phone off/on and that didn't do anything.
iPhone 6s, iOS 9.3.2