If you have tried a replacement screen and it is still the same it would point to one of the touch IC’s becoming faulty and will need to be replaced. This will require microsoldering so you will need to have the proper equipment, schematics, board view software and some experience.
The first thing you need to do is determine which of the two touch IC’s has become faulty by using a multimeter in diode mode on the two connectors. You will be looking for an open line or short, once you have found it you will need to replace the touch IC the line goes to.