Issue description: When I tried loading into my modded world after adding RFTools, it shows that it's using the backup level.dat. Loads into the world for a split second(can see the skybox) and then crashes to desktop.

Steps to reproduce: Loading into the world with rftools always tells me its using the backup level.dat and crashes, removing it fixes it. Doesn't happen when generating a new world.

Versions:

• Minecraft:
• Forge: [1.12] 2838
• McJtyLib: 1.12 - 3.5.3
• RFTools: 1.12 - 7.71

Am using optifine, removing it didnt seem to have any effect.

Didn't try disabling other mods because I can't without destroying stuff in my world, although it looks like biomes o plenty might seem to be part of the issue?

Relevant logs, if any:

https://pastebin.com/nxauqc0k - full crash report

Sorry if this is a bit vague, if you need me to I can try disabling each mod one at a time, when I get the time.

I'm on vacation right now but that I don't think rftools is to blame here as there is literally nothing rftools does that has to do with level.dat. btw did you also add mcjtylib?

Two things:

1. It looks like you're on to something with Biomes O'Plenty. Please try removing it and posting the new crash report without it if it still happens.
2. Do you have a lot of mahogany doors in close proximity in your game world? If you break or separate them, does that make the crash stop happening?

Question. Do you have notenoughids? If so that's likely the reason as this mod can have issues with mods being added or removed

I didn't have any mahogany doors placed. I had notenoughids installed at one point but I removed it because it was causing a conflict with another mod. And yes I had mcjtylib, I tried removing just rftools and it fixed the issue. I'll remove BoP and get back to you when I get the time. Also a note, I recreated the same world with the same seed and brought all my stuff from my old world at the same location, and there's no crash, so it must have been something in the world I placed that caused it.