The issue may improve by updating the unit.
If the version of the software of your unit is ver.1.02 or earlier, try to update the software of the unit.
When updating the software to the latest version, the response of the touch panel will improve.
Software update for NW-A series:
Moreover, due to the nature of the touch panel, it may not respond or you may feel that the sensitivity is bad depending on how you touch it. In this case, touch the center of the icon firmly from directly above. Especially, as the icon located in the lower part of the screen is small, be sure to touch it correctly.