Do you ever just reboot your phone or do a Soft Reset? This helps your system stay running smoothly. To Soft Reset, start from powered on and hold the Volume Down + Power buttons until the phone reboots. You do not loose data.
If the problem persists you may want to try a Hard Reset. You will loose data doing this so make a backup first so you can restore it during the setup.
Nokia Lumia 1320 hard reset
Last resort is to restore the Official OS and Firmware with Lumia Software Recovery Tool. This too causes a data wipe,
http://download-fds.webapps.microsof...lInstaller.exe
A side question: are you running the Preview for Developers? That can cause anomalies in behavior. If so, you may want to go straight to the Recovery Tool if Soft Reset doesn't help.