My brother and I were playing on his survival world, pure survival with no cheats or creative mode. When he traveled from the Overworld into the Nether through a portal he had used before and I had just exited, his screen stopped on the loading screen of entering the Nether and the damage sound was playing, as if he was taking damage from suffocation. He couldn't pause or anything, while I could still play like normal on my screen. Soon, he died and dropped all his items but after checking both the Overworld and the Nether we couldn't find his items anywhere, even after digging under the portal in case he glitched into the ground. One of our friends from online was also on the world, in case that might've been part of the problem. Please find out what happened and fix the problem. Thanks.