while uncommon in iPads, it is possible that its the touch sense chip on the mainboard. That would really only make sense if the iPad got wet or had a bad drop.
If it were me, I'd try cleaning the digitizer connectors and the motherboard connectors with 99% IPA. Flood them and then let them air dry. Check for any damaged teeth on the connectors and if they look good, plug it all back in and give it a test. Also, the metal pieces on the back of the connectors likes to bend upwards, making it impossible to get a proper seating. Make sure that piece of metal is straight.
If that doesn't fix it, its probably the touch sense chip.