Acer Chromebook 14 CB3 431, screen flicker when moving screen

It's likely an issue with the cable that goes between the motherboard and the display. It's routed through areas near the hinges and gets flexed each and every time you open or close the Chromebook. This can, over time, either pull the cable partially out of the connector at one end or start to break some of the wire strands where the cable is flexed. If the problem is the former you can just pop it apart and fully plug in the cable ends, perhaps adding some tape to help hold them in. If it's the latter the fix is to replace the cable. Either requires skills needed for laptop tear down and reassembly and a good grounded work surface along with a grounding strap used by the technician doing the repair.