Touchscreen will occasionally not work

My LG G Vista is having a problem where the screen will totally stop responding for varying periods of time. However, after locking & unlocking the phone several times, it will generally start working again. Sometimes I have to restart it by removing the battery.

So far, I have booted the phone in safe mode, and have removed the SIM card. However, neither of those has helped. Any thoughts?

Thanks a bunch!