@gabrielblauth not every display error will show externally. I would at least start with the screen. Of course, make sure that all cables are still properly seated and did not get dislodged etc. It's always best to remove them from the connector and then reinsert them just to verify, proper connection is made.
GO to the device page [[Topic:sony a6400]] and scroll to Documents. There you'll find the service manual for the camera. It will help you with the repair of the LCD. While you are disassembling it, double check all flex cables and check for any unusual or damaged looking components.