Chosen Solution
I repaired my iPhone and it was really dusty inside so I’m thinking the contacts are dirty. The rest of the screen works just not the left side of the screen.
Chances are that this is a defective replacement screen. However, as you noted, if the inside is very dusty, check the connectors to insure they are free of debris. I would also re-install the original screen, if it still “worked” to see if the problem is consistent with the screen or the phone.
