This happened twice in my world when i was playing with my friends. The first time when she enter through a portal she said that she died in the loading screen as she traveled through the portals. And at first we thought it was just a glitch but it happened a second time which another friend of mine died in the loading screen as she was traveling through the portal and each time it said "player suffocated" and also each time both lost their items and was also traveling from the nether to the overworld and it happened in two different portals.Also weirdly each time the portals they died have a boat at the other end or a sheep at the traveling end.