My phone has this problem occasionally. I know how to stop it, I am just annoyed it does it. because the fix is not permanent.
Whenever my phone starts to lag or be slow to come out of screensaver, I restart it.
After the reboot, It starts to update apps that required updating. The issue doesn't recur again until an app that is set on auto update needs to be updated again.
The frustration is mostly because when it lags so much from coming out of screensaver that it wont let give me enough time to unlock it, then the Lifeproof case has to be pried open, then battery reset, then clean the Lifeproof case screen protector... etc.