In case of having touchscreen issues with your LG G2, like touchscreen being unresponsive for short periods of time, you can try to turn off the screen first for about 5 seconds and turn it back on. If the problem persists, reboot the phone by holding down the power button until you see the phone rebooting. Have in mind that the touchscreen issues could be due to the motherboard. In that case, it is necessary to locate the problem or simply replace it. If you still having problem with the screen you could replace it. For this, you can use the LG G2 VS980 Touchscreen Replacement Guide.