agree to check the wiring. I'd start at the punchdown connectors. They're great for a nice stable connection, but if you plug and unplug and replug enough times, especially with a larger cable like an HDMI one, they can work loose. If the cat 6 isn't inside conduit, then there could be rodent issues as well, so you'll probably want to do a continuity test from end to end. good luck!