Getting an error like this;
java.lang.IllegalArgumentException: ChunkNibbleArrays should be 2048 bytes not: 0
at net.minecraft.world.chunk.NibbleArray.<init>(SourceFile:16)
at net.minecraft.world.chunk.storage.AnvilChunkLoader.func_75823_a(AnvilChunkLoader.java:450)
at net.minecraft.world.chunk.storage.AnvilChunkLoader.checkedReadChunkFromNBT__Async(AnvilChunkLoader.java:129)
at net.minecraft.world.chunk.storage.AnvilChunkLoader.loadChunk__Async(AnvilChunkLoader.java:93)
at net.minecraftforge.common.chunkio.ChunkIOProvider.run(ChunkIOProvider.java:70)
at net.minecraftforge.common.chunkio.ChunkIOExecutor.syncChunkLoad(ChunkIOExecutor.java:92)
at net.minecraft.world.gen.ChunkProviderServer.loadChunk(ChunkProviderServer.java:118)
at net.minecraft.world.gen.ChunkProviderServer.func_186028_c(ChunkProviderServer.java:89)
at net.minecraft.server.management.PlayerChunkMapEntry$1.run(PlayerChunkMapEntry.java:39)
at net.minecraftforge.common.chunkio.ChunkIOProvider.runCallbacks(ChunkIOProvider.java:134)
at net.minecraftforge.common.chunkio.ChunkIOProvider.syncCallback(ChunkIOProvider.java:96)
at net.minecraftforge.common.chunkio.ChunkIOExecutor.syncChunkLoad(ChunkIOExecutor.java:94)
at net.minecraft.world.gen.ChunkProviderServer.loadChunk(ChunkProviderServer.java:118)
at net.minecraft.world.gen.ChunkProviderServer.func_186028_c(ChunkProviderServer.java:89)
at net.minecraft.server.management.PlayerChunkMapEntry$1.run(PlayerChunkMapEntry.java:39)
at net.minecraftforge.common.chunkio.ChunkIOProvider.runCallbacks(ChunkIOProvider.java:134)
at net.minecraftforge.common.chunkio.ChunkIOProvider.syncCallback(ChunkIOProvider.java:96)
at net.minecraftforge.common.chunkio.ChunkIOExecutor.tick(ChunkIOExecutor.java:150)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:728)
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:397)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
at java.lang.Thread.run(Thread.java:748)
If you have a world that was generated in Minecraft version 1.13 or above and are you trying to run this world on a 1.12 or lower then it won't work. You cannot under any circumstances run a 1.12.2 server with a 1.13 or above world it just won't work.
Suggestions;
Create a new world by deleting or renaming the current world (to save later)
Uploading a 1.12 world so that your 1.12 server can work.
Please reach out to us on live chat if you require any further assistance, We take backups every day for 14 days so if you've done something by mistake and no longer have your files! We can help assist in restoring your server as an emergency!