In the past hour, I've had all the contents dissapear from a lime green shulker box and a brown shulker box disappear into thin air. After my brown box dissapeared, my inventory became bugged and I couldnt move anything around it. (I lost my brown box in my storehouse and my green box got wiped on my boat. I left the green box on the boat deck where it got wiped, but the brown box is MIA.)
At the time I used the backpack function gotten from /menu, where you do shift+right click to open a shulker box without having to place it. The feature worked just fine until today.
The brown box had building supplies and my lime green box had many valuable tools and items including vote keys.
I encourage people to not use the shulker backpack until further notice.