Put the summary of the error you have here

What I expected to happen was ...: "
That the shulker box kept my things in the base where you appear in the end that is obsidian

What really happened was ...: When I entered the end my shulker box was lost and I cut off the water I had as if I had reset that area

I have put a shulker box in the obsidian base that is generated when you enter the end and in that shulker box I kept many important things in what I built something and I left the end and when I returned it was in less than 4 minutes the shulker box had disappeared along with my things and I had put a bucket of water, I noticed that that bucket of water every time I entered if I left it on the water disappeared and I think that area or something like that is reset
Steps to reproduce:
1. ... Put the shulker box on the obsidian base on the end or a bucket of water
2. ... get the end and come back