Players lose your items when sometimes join the world

It happened 5 time with me. Players can sometimes lose their items, xp and when joining the game, they spawn in the original spawn of the world, not in their bed (they have already joined other time the game). Please fix it, this bug is making my friends lose their items in my world, like armor, swords and equipments.
(I put iPhone 6, but this bug is on iPod and iPad too)