Go into phone settings and scroll down to apps. Tap to select apps. Then scroll down to stock android, and tap to select. Then tap to select notifications. You will see 4 switches on that screen. Turn all 4 switches to the off position. Then reboot your phone. If the pop-up is still there, go back into stock android settings and tap storage. Delete data storage and clear cache. After rebooting, you will need to set shortcuts back up on your home screen, but you shouldn't have any more problems.