If you have items in a chest and you put a dye on it it removes all the items that are in the chest.

If it is any 6.0 version, the CurseForge page does state
6.0 Fabric, Forge and NeoForge 1.20.1 and 1.20.4

Chest / Barrel contents are removed when dying to a different colour, please update to 6.1

what version