I had spent some good time farming ancient debris for the netherite armor/gear hustle.

I put all netherite gear in my inventory to include pickaxe, sword, chest, head, legs, and feet.

Next, I went to select/swap my then worn damaged diamond chest plate and netherite chest plate.

Click

Client crashed.

Logged back in, and all netherite related items in my inventory were GONE.

I lost hours of work and materials crafting this.

I recall something similar happening before, leaving me with a potential theory. 

I didn't unequip the diamond chestplate first, which seems like a key element here.

I selected the netherite armor and tried to "swap" it with the worn diamond plate on my paper doll.

I will gladly work with you to get this resolved, as I believe this bug may still exist in other non beta versions as well.