I found several threads asking for solution of malfunctioning touchscreen: erroneous fingers detection, device lock, other issues.
- too many/low light in environment (!)
- too high/low battery
- wrong firmware
- bad mounting of screen cable
- bad calibration
My device locked several times a day due to screen malfunction.
I dismounted my G9 (quite hard, it's so tight that I thought there were hidden screws, but they weren't: "just" 20 plastic clips!)... and now it is working quite good: screen is still not precise, but device never locks up.
I keep it dismounted, holding it by duct tape!
Enable developer options to show both pointer position and finger position: you'll see a filled circle in the point you touch if you only enable second option, but if you check the first one you'll see a vertical and horizontal line passing through the center of the circle, and an additional empty circle with varying size depending on pressure strength (!); additionally, on top of screen you'll see:
number of points/fingers
Study these parameters to see how bad your screen is responding!
Firmware: original (Android 4.0.28 (android 4.0.4), OMAP OMAP4460 ES1.1, Start version unknown/5.05.000009 - C0x00, build IMM76D)