Pretty sure it was a loose cable. They’re basically giant iPhones and I saw similar issues on those. I should also mention said counter had an antistatic mat on it to soften the blow.

I was an apple tech for a time. With iPads that were out of warranty (basically go buy a new one or GTFO) and exhibiting a certain display issue, I would take it in the back and slam the thing on a counter at a certain angle. Worked every time for that particular problem.