Issue Description:

ViaFabric shows some items from a 1.21.1 client --> a 1.12 server, but not all of them.

What happens:

Several items are just blank on the server I'm on, and it's fairly random:

• Firework Rocket
• Wither Skeleton Skull
• Oak Signs

Here are some screenshots of shulkers:

vs

What you expected to happen:

These items would show up...

Steps to reproduce:

This is a headache.

1. Install a 1.21.1 client with ViaFabrcPlus.
2. Create a 1.12.2 server.
3. Give yourself a shulker box with the impacted items I listed above.

...

Affected Versions (Do not use "latest"):

• ShulkerBoxTooltip:
• Minecraft: 1.21.1
• Fabric Loader: 1.16.9
• Fabric API: 0.107.0+1.21.1
• Other mods (if relevant): in the logs lol

Your most recent log file where the issue was present:

https://mclo.gs/NQuMGrc

I found this also occurs with cobwebs.
Note: when a shulker is full of items that don't load properly, it appears empty.

This seems to be related to The Flattening. Items with IDs that were changed from 1.12.2 to 1.13 don't show up properly, as far as I can tell. (this also occurs with logs and dyes)

This is an interesting issue for sure...
I'll see what I can do on my end to fix this, but no promises.

It seems to also occur with other mods using ViaFabricPlus being unable to render items from pre-flattening. Honestly not sure if this is an underlying issue with VFP or not, but thanks for the help!