I was in towny and decided to protect my Hogwarts items by placing them into a shulker box. I placed My wand, my Pande doll, my Hari doll, my broom, several gobstones, several books, floo powder, and a stack of 15 cauldron cakes.
I broke the shulker and went about my business.
When I reopened the shulker the cauldron cakes were unstacked and some of the items that I put in the shulker were overwritten. The only items I care about that were lost are my pande doll and my wand.
I entered towny.
Began collecting supplies and mining.
Placed down the empty shulker.
Shift clicked several items into the shulker, including the stacked cauldron cakes.
Closed and picked up the shulker.
Replaced the shulker.
Found it with the unstacked cauldron cakes and the other items missing.