not all mobs wear armor. Based on difficulty, the percentage chance of the mob being able to pick the item up increases. IN this case, you have 3 skeletons that can't pick up items
I Just tried it, and I experienced the Same Bug, Remove the Invulnerable tag, that fixes it.
not all mobs wear armor. Based on difficulty, the percentage chance of the mob being able to pick the item up increases. IN this case, you have 3 skeletons that can't pick up items