Some inventories don't display items at all

[BlitzOffline]

Some inventories (tested with LOOM and ANVIL), Don't display the items they're supposed to.
They do execute the actions and check requirements.

I found a post about this from 1.15.2: https://www.spigotmc.org/threads/set-item-inside-a-loom.445807/
According to it, some inventories that don't store items like furnaces, chests, etc., can't have items inside using just the spigot API. Tho from their testing this also happens with crafting table (Crafting tables work for DeluxeMenus).

I don't really know what we should do. We have a couple options:

• We remove support for those inventory types completely.
• We leave them as they are with invisible items but actions still working
• We use packets and maybe get them to work somehow?

This was my test menu: https://paste.helpch.at/avocumofuh.bash