Attribute modifier backup doesn't properly restore 1.21 modifiers

[kennytv]

'/viaversion dump' Output

https://dump.viaversion.com/ede8d9a211e8968429f085bb52cd761d1597a77222b368dd6649d49a9bce7e0b

Server/Client Error

No response

Bug Description

Getting an item with custom attribute modifiers on 1.21 does not have the original item restored when using creative mode and moving the item around in the inventory, see in- and output: https://i.imgur.com/cqucxzx.png

Steps to Reproduce

Log in with 1.20.4, use creative mode, move item with attribute_modifiers around, check item data again

Additional Server Info

No response

Checklist

• Via plugins are only running on EITHER the backend servers (e.g. Paper) OR the proxy (e.g. Velocity), not on both.
• I have included a ViaVersion dump.
• If applicable, I have included a paste (not a screenshot) of the error.
• I have tried a build from https://ci.viaversion.com/ and the issue still persists.

[Barvalg]