I bet the root cause is voltage/amperage. Not disputing what Jeep Momma wrote, but her hard work and testing supports my theory in that the factory wiring is not thick enoug to deliver enough bang to the lights, and since LED's are very picky when it comes to feeding them (hence the recommendation for anti-flicker boxes), they do whatever the hell they choose to when the voltage is low.
Oddly enough, lower voltages need weirdly thick wires to transfer power over longer distances, and even three feet is a long distance for 12 volts. Looking at my 2016 wranglers headlight wiring (factory), it's no wonder the lights are sub par. Definitely should bump up a gauge or two.
OP's problem probably is that selecting gear bumps voltage just a tad bit, enoug to trigger the lights.