Front camer flex causing short circuit?

You could have a defective replacement flex. Small parts are well known to suffer from poor quality, especially if ordered through non-reputable vendors (cough!...eBay). So ideally, you need to try another, preferably known-good part to eliminate that possibility.

I would also check the FCAM FPC connector on the logic board to see if there is any debris or damaged pins. Finally, there could be damage on the logic board itself. It would help if you posted more info on the background of the phone. Why was it repaired in the first place, was the phone dropped or came into contact with water etc.