Even though it's not present when you graph, it's still ribbon cable failure. Unfortunately, unless you have a soldering iron, there’s nothing you can do to fix it. There’s a guide over on the Cemetech (calculator forum) that addresses this: https://www.cemetech.net/forum/viewtopic.php?t=5161
The TI-84 Plus is far more difficult to fix than the TI-83 Plus. However, if you're experienced, there's a tutorial here: https://youtu.be/b5ym1xhbJjc