Lost my stuff in Minecraft?

Hi,
I'm sorta an intermediate player when it comes to Minecraft. Anyway playing in survival mode, I had some good items in my backpack and was heading back to my base. I saw quite a deep cavern with some iron ore in it so I went down and mined. I wasn't planning to stay down there for long but then this witch came up behind me and killed me. I lost all my stuff and I didn't know exactly where I was when I died and I lost my map and compass in the process. I had to save & quit after that and so I just got back on. I finally found the cavern where I lost my stuff. Looking down from the surface I could see all my stuff and my experience orbs on the floor of the cavern. Once I made my way down all the stuff was gone? And I'm pretty sure I was in the exact place where I saw it like 2 minutes ago? Why did my stuff disappear and is it gone for good?

Thanks

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