It happened when I fought the dragon first time in my life and I clicked the dragon egg it teleported on the end portal and breaked and teleported through the end portal to overworld and I tried to find it at all places at spawn point 0,0 and at my bed I think it despawned and I find the similar think at youtube and he told that it have teleported to the sky up to 33000 blocks and it ruined my life's first end fight mojang should fix it quick or make an feature that if dragon egg gets destroyed it should teleport back to the end