I'm anything but knowledgable when it comes to such issues so I'll just explain what I'm doing:

I place two 🎄 Christmas Trees, one Green one and decorate it fully then I place a another Christmas Tree, this time a white one and fully decorate it.

Then, I save the world and close the game, start the game up again and join the world.
Sometimes I instantly get following error or sometimes I spawn in to my Christmas Trees being either:

• gone (thanos snapped outta existence)
• missing ornaments (like they were never there)
• them just being the same like how I left them

The last one just means that I will experience that error on my third-fourth load into the world

The only way to regain access back to the world is by going into the world files -> entities and removing everything in there which isn't ideal 'cus it removes every entity that you had there (armor stands, item frames etc.)

MC version: 1.18-rc3
Fabric Loader version: 0.12.5
Fabric API version: 0.43.1+1.18
Christmas Spirit version: 1.1.0-1.18
Mods loaded: Architectury, Christmas Spirit, Cloth Config v6, Fabric API, Roughly Enough Items
OS: Windows 10 x64
Log file