(Updated March 1st, 2017 - Update on the M1 pad jumper and the possibility that we have a true fix!)
In Apple's ongoing quest to make their devices ever thinner, an unexpected problem crept into the design. The repair community started seeing cases of iPhones that, intermittently, were losing touch functionality. At first, the phone will typically develop intermittent touch control failure. For some phones, a gray/white bar starts appearing at the top of the screen. Twisting and applying pressure in certain spots sometimes allows touch control to work for a short period of time, but eventually, the touch interface ceases to function entirely. Today, it is colloquially known as Touch Disease.