Minecraft said it was out of memory when i tried to open a world i got at the minecraft marketplace. however, it let me open a world without a mod.

hi! I love Minecraft. however, I found a bug in it. a few days ago, I bought a world with a lucky blocks mod from the marketplace. I started to make a lucky block race. I left the world and came back the next day to work on it. Minecraft said that I ran out of memory, but I was able to create a new world and build something in it! please fix this issue as soon as possible, because my friends wanna play the lucky block race!