It's modded.

 

 

---- Minecraft Crash Report ----
// Don't be sad, have a hug! <3

Time: 12/19/19 12:47 AM
Description: Exception in server tick loop

java.lang.ArrayIndexOutOfBoundsException: -5580619
    at java.util.ArrayList.elementData(Unknown Source)
    at java.util.ArrayList.set(Unknown Source)
    at net.minecraft.world.chunk.storage.RegionFile.<init>(RegionFile.java:94)
    at net.minecraft.world.chunk.storage.RegionFileCache.func_76550_a(SourceFile:64)
    at net.minecraft.world.chunk.storage.RegionFileCache.func_76549_c(SourceFile:110)
    at net.minecraft.world.chunk.storage.AnvilChunkLoader.loadChunk__Async(AnvilChunkLoader.java:82)
    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.world.gen.ChunkProviderServer.func_186025_d(ChunkProviderServer.java:135)
    at net.minecraft.server.MinecraftServer.func_71222_d(MinecraftServer.java:344)
    at net.minecraft.server.MinecraftServer.func_71247_a(MinecraftServer.java:314)
    at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:270)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:486)
    at java.lang.Thread.run(Unknown Source)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- System Details --
Details:
    Minecraft Version: 1.12.2
    Operating System: Windows 10 (amd64) version 10.0
    Java Version: 1.8.0_211, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 8023419760 bytes (7651 MB) / 8741978112 bytes (8337 MB) up to 9544663040 bytes (9102 MB)
    JVM Flags: 2 total; -Xmx10G -Xms8G
    IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
    FML: MCP 9.42 Powered by Forge 14.23.5.2847 4 mods loaded, 4 mods active
    States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored

    | State  | ID        | Version      | Source                                  | Signature |
    |:------ |:--------- |:------------ |:--------------------------------------- |:--------- |
    | LCHIJA | minecraft | 1.12.2       | minecraft.jar                           | None      |
    | LCHIJA | mcp       | 9.42         | minecraft.jar                           | None      |
    | LCHIJA | FML       | 8.0.99.99    | forge-1.12.2-14.23.5.2847-universal.jar | None      |
    | LCHIJA | forge     | 14.23.5.2847 | forge-1.12.2-14.23.5.2847-universal.jar | None      |

    Loaded coremods (and transformers):
    Profiler Position: N/A (disabled)
    Player Count: 0 / 20; []
    Is Modded: Definitely; Server brand changed to 'fml,forge'
    Type: Dedicated Server (map_server.txt)

crash-2019-12-19_00.47.15-server.txt

I have no back up but thank you.