Missing items

Hi,

1. I had a half of shulker box of TNT I was in the nether using it I get lagged out. I log back on and the TNT shulker box is gone no where to be found not anywhere I put it. It just vanished. That TNT took a long time to farm up. A week of farming gone just like that. My Internet connection is just fine I double checked. I'm not sure why that happened but I hope I can get my shulker box back.