Inventory De-spawn Impossible Death

I was exploring a cave with my daughter, we were on a hunt for Diamonds, we had made pretty good progress, it was a huge cave, and multiple layers. We were using a mixture of water buckets and torches to descend to the bottom. Anyway, I had some enchanted equipment, a pickaxe with mending, efficiency V, fortune 3, and unbreaking 3. The other weapon I was carrying was a sword, Sharpness 5, unbreaking 3, knockback 2, and mending as well. My inventory was full, many stacks of cobblestone, basalt, and deep slate, as well as maps to get to our different destinations.

I was in full iron armor, had a map in my off hand, and I was attacked by a witch. I of course could not see where he/she had thrown the splash damage from, so I dug into the cave wall, only large enough to fit me, a one by two nook, where I immediately turned around and put a wall up for my protection. I waited for the poison to run out, and then my health healed to half full. I could hear the witch right outside the blocks waiting for me, so I switched to my sword and prepared for battle. I removed the top block of my temporary wall and was immediately pummeled by another splash damage potion which insta killed me, (I had 32 levels at the time from mining, a couple stacks of raw iron, and 37 diamonds.) 

I was super familiar with the cave at this point, and there was still a block on the ground, so there was no way the mob could have gotten close enough to grab anything, or any other mob. As I mentioned, I had dug straight back, and I was enclosed in a 1x2 (1 wide, 2 tall) little nook, so I was not worried about my items being lost, sad about the xp, but the items I had worked hours for would still be there. It took me about 1 minute to get back to where I died, and to my astonishment, everything had de-spawned immediately except a partial stack of cobblestone, my iron armor, and the map (the things that were on my person and not in my inventory.) All of my weapons were gone my pickaxe was gone, all raw materials were gone, and all maps but one I had in my off hand were gone.

We play on a realm, so the kiddos can jump in and out whenever they desire, but this is not the first time our items have de-spawned randomly. It happens all the time in realms specifically, we jump out of boats and they temporarily disappear as well, which is a HUGE pain when deep sea diving. This however, was the unforgivable that made me have to come here with my rant about the bug, as I had spent hours fishing, and killing, to enchant my items, and then they were gone in an instant. Please help