It is difficult to address the issue because it is a strange problem, but from your story it seems your problem arises from the system connector ( charging port), so try these steps. 1- switch off the device and remove dust/dirt/lint from the port with a paper clip or large needle because it could be causing a short which interferes with the digitizer. Run the paperclip sideways very lightly across the contact points to clean the contacts. 2- open the device and clean the contacts on the home button and press and tape the flex connector at the bottom of the device to ensure proper connection. 3- check that digitizer connector is properly connected. 4-replace digitizer
I had the same problem. Check the old lcd, it has a small rubber with 2 holes where the proximity sensor fits into, it aligns and holds the sensor in the proper position. This is why so many people have this problem because its unnoticeable at a quick glance. Guaranteed this will fix your problem.