[06:35:15 ERROR]: Couldn't save chunk; already in use by another instance of Minecraft?
net.minecraft.server.v1_12_R1.ExceptionWorldConflict: Failed to check session lock for world located at .\pernicious, aborting. Stop the server and delete the session.lock in this world to prevent further issues.
        at net.minecraft.server.v1_12_R1.WorldNBTStorage.checkSession(WorldNBTStorage.java:85) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.World.checkSession(World.java:3006) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.ChunkRegionLoader.saveChunk(ChunkRegionLoader.java:152) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.ChunkProviderServer.saveChunk(ChunkProviderServer.java:257) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.ChunkProviderServer.unloadChunk(ChunkProviderServer.java:416) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.ChunkProviderServer.unloadChunks(ChunkProviderServer.java:354) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.WorldServer.doTick(WorldServer.java:309) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:905) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:423) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:774) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:666) ~[patched_1.12.2.jar:git-Paper-1618]