If you haven't already done a full restore, try this first. Goto Settings, select apps (all) and scroll to Launcher. Select it and then clear cache, then clear data. Then hold power button down until it shuts off and begins reboot sequence. Once reboot starts let go of power button and let the device reboot itself. This is a hard reset and between that and clearing out the junk in the launcher you might solve your problem. As a last resort do the factory reset.
Often when upgrading to a major OS upgrade a lot of junk from the old OS remains in the system cache and needs to be removed in order for the device to function properly. Good luck.