iPhone 6 Plus touch not working properly, touch IC already replaced

That’s an interesting problem indeed. A known-good screen, M1 jumper, new IC’s, proper readings on the connector and yet the exact same dead spot. I would surmise the issue is with the pins that allow the two IC’s to communicate to each other. That’s the only part of the circuit you have checked.

Meson has a series of 24 pins labeled: SAGE_TO_TOUCH_VSTM_OUT and a series of 15 pins labeled TOUCH_TO_SAGE_SENSE_IN. They are driving the X-Y grid of capacitive touch sensing elements of the digitizer. Essentially, they track your touch, multi-touch and gestures. When you touch the panel, Meson does some magic and sends the raw data out to Cumulus via the SAGE_TO_CUMULUS_IN lines. These are the lines you have not checked and they are interconnected with the “trailer park” capacitors between the two IC’s. I would start by checking if those caps are dislodged and then test them to insure they are good (not shorted). In a worse case scenario, an inner trace could be damaged so that would require that you probe the pads directly underneath the IC’s.