When I join my friend, I load terrain, my inventory loads, then up to 2 seconds later my game freezes before eventually I am booted from the server. The text that shows up is "Internal Exception: java.io.IOException: an existing connection was forcibly closed by the remote host." This was using the Permafrost modpack in version 1.16.5, forge version 36.2.23. I am able to run the game in singleplayer. I'm not sure what is causing it, but in the log file, I found a seemingly repeating fatal error message that I'm not sure what it means or how to fix it. This repeating error is shown at the bottom of this text. This has happened in other modpacks with us before, and I want to find a fix. I tried to figure it out on my own, but I'm lost at this point. Any help would be appreciated. I attempted to add the JVM arguments in the "Java and you: How to avoid crashes" guide, but it prevented minecraft from launching. I've also tried using forge version 36.2.39, but the exact same thing occurred.

[21:44:42] [main/FATAL]: Error executing task on Client
java.lang.IndexOutOfBoundsException: null
    at io.netty.buffer.EmptyByteBuf.readUnsignedByte(EmptyByteBuf.java:536) ~[netty-all-4.1.25.Final.jar:4.1.25.Final]
    at net.minecraft.network.PacketBuffer.readUnsignedByte(PacketBuffer.java:753) ~[?:?]
    at net.minecraftforge.fml.network.simple.IndexedMessageCodec.consume(IndexedMessageCodec.java:155) ~[?:?]
    at net.minecraftforge.fml.network.simple.SimpleChannel.networkEventListener(SimpleChannel.java:80) ~[?:?]
    at net.minecraftforge.fml.network.simple.SimpleChannel$$Lambda$2947/1393423275.accept(Unknown Source) ~[?:?]
    at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:247) ~[eventbus-4.0.0.jar:?]
    at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:239) ~[eventbus-4.0.0.jar:?]
    at net.minecraftforge.eventbus.EventBus$$Lambda$2949/863026773.invoke(Unknown Source) ~[?:?]
    at net.minecraftforge.eventbus.EventBus$$Lambda$3122/1079430578.invoke(Unknown Source) ~[?:?]
    at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302) ~[eventbus-4.0.0.jar:?]
    at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283) ~[eventbus-4.0.0.jar:?]
    at net.minecraftforge.fml.network.NetworkInstance.dispatch(NetworkInstance.java:86) ~[?:?]
    at net.minecraftforge.fml.network.NetworkHooks.lambda$onCustomPayload$1(NetworkHooks.java:91) ~[?:?]
    at net.minecraftforge.fml.network.NetworkHooks$$Lambda$15976/1944764788.apply(Unknown Source) ~[?:?]
    at java.util.Optional.map(Optional.java:215) ~[?:1.8.0_51]
    at net.minecraftforge.fml.network.NetworkHooks.onCustomPayload(NetworkHooks.java:91) ~[?:?]
    at net.minecraft.client.network.play.ClientPlayNetHandler.func_147240_a(ClientPlayNetHandler.java:1904) ~[?:?]
    at net.minecraft.network.play.server.SCustomPayloadPlayPacket.func_148833_a(SCustomPayloadPlayPacket.java:59) ~[?:?]
    at net.minecraft.network.play.server.SCustomPayloadPlayPacket.func_148833_a(SCustomPayloadPlayPacket.java:11) ~[?:?]
    at net.minecraft.network.PacketThreadUtil.func_225383_a(SourceFile:21) ~[?:?]
    at net.minecraft.network.PacketThreadUtil$$Lambda$16299/1812077582.run(Unknown Source) ~[?:?]
    at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(SourceFile:144) [?:?]
    at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23) [?:?]
    at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:118) [?:?]
    at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(SourceFile:103) [?:?]
    at net.minecraft.client.Minecraft.func_195542_b(Minecraft.java:948) [?:?]
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:607) [?:?]
    at net.minecraft.client.main.Main.main(Main.java:184) [?:?]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_51]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_51]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_51]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_51]
    at net.minecraftforge.fml.loading.FMLClientLaunchProvider.lambda$launchService$0(FMLClientLaunchProvider.java:51) [forge-1.16.5-36.2.23.jar:36.2]
    at net.minecraftforge.fml.loading.FMLClientLaunchProvider$$Lambda$494/783339262.call(Unknown Source) [forge-1.16.5-36.2.23.jar:36.2]
    at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-8.0.9.jar:?]
    at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-8.0.9.jar:?]
    at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-8.0.9.jar:?]
    at cpw.mods.modlauncher.Launcher.run(Launcher.java:82) [modlauncher-8.0.9.jar:?]
    at cpw.mods.modlauncher.Launcher.main(Launcher.java:66) [modlauncher-8.0.9.jar:?]

The version you are using is no longer supported on this forum.

Please update to a modern version of Minecraft to receive support.