Players who are non-OP cannot place chests with NBT data attached. It can be done in Vanilla no problem, but it seems to be something Spigot related. I usually do crate drops for my players on a timing system, but when they place the chests, they are empty. If they set and break, it's empty. Only if an OP sets it will it work. It is quite useful for servers to give loot boxes using loot tables.