[JA]

I think it may have something to do with LED flicker being picked up by the imaging system. It may be that pulse width modulation is used in the dimming circuit of the lamp or there is AC in its power supply. To the human eye with its relatively slow response the light may appear continuous and appears as always ON, but if recorded with video or a suitably short exposure you may, if I'm correct see the truth of a changing illumination pattern, some rows on, others off then changing....possibly. Why others may not see this phenomenon would depend on the nature of the LED source and camera type and exposure. Try increasing the exposure duration in steps say: your initial setting, then 2x, then 4x, then 8x.... what differences do you see? If you see a more integrated or whole pattern as you increase the exposure duration that is a sure sign of what I suggested. You could also use an incandescent light source with white diffuser or t-shirt to verify that its the LED light source which is the issue due to its inherent flicker/fast response compared with the pedestrian speed of an incandescent source. If that shows no change (lines still present) then it's a camera issue or interaction

It could also be an interaction / sort of interference effect between the led row pattern and the camera pixel pattern and associated frame rate/exposure duration and refresh rate.
Best
JA