Please follow below steps for troubleshooting：
1. Update firmware to the latest version：" Settings " > " About " > "System Update " > " Check update "
2. If it only happens when you execute some specific applications ,please try to update, reinstall or to uninstall the app.
3. Access to Safe Mode ( long press power key > tap and hold " Power Off " > " OK ") ：If your device works well in safe mode, malfunction might be caused by 3rd-party apps. Please reboot your device to check again if it works well.
4. Backup your data and perform factory data reset.
Note: Once RESET was performed, all data, apps, settings and personal information will be deleted after initialization.
If above steps can't solve your issue, please contact ASUS Customer Center for help.
