As of the newest 1.17.1 Pre-release 3 this bug is fixed, but couldn't find any documentation of it on the bug tracker, putting a /item replace entity (current entity) (specified container) with (specified block/item) into a repeating command block would make it seem like the item in the container is not constantly being filled in the inventory. If you hold down Q it will still refill the container but it looks like there is no item in the specified container.