End Obsidian Platform problem

I went to the end with some building planned, as I needed to build from the obsidian platform that I spawned on to the main island.

So, naturally, I brought my Ender Chest filled with my tools, and a shulker box filled entirely with stone bricks. I placed those down as soon as I arrived, and got to work building.

About 1/4th of the way through building, I noticed that my pick had low durability. The nearest anvil was at my house. So I went through the end portal and to my house to repair it, and then returned to the end.

Upon returning, I found that both my ender chest, and my shulker box filled with stone bricks were gone from the platform. Has anyone else experienced such a thing? Is there any way to get them back? I worked way too hard for the stone bricks for them to just be gone. Any help or ideas are very much appreciated.