This is a Preview bug. I repeat this is a Preview bug. Preview is used here because this is a Java snapshot for Bedrock. The issue was revealed while trying to join a world in Minecraft Preview. It wouldn't let me join the specific player Calvin8253's world. Actually Calvin8253 has more worlds than one that I couldn't join. Probably I couldn't update, which actually was the reason I could only join my worlds. Please update my preview game, Mojang, please. Also please click the picture. It shows the reason.