Using a custom loot table, luck has an impact on drops (by design) when applied to a single chest. Placing 2 chest side-by-side (double chest) has loot drops for both chests but the results are not impacted by luck. If a shulker box is used instead, the loot drops are also not impacted by luck.

I've attached a very basic loot table to show the issue. You'll need to open it as a chest with luck amp 0 and without on a chest, double chest and shulker box.