internal exception io.netty.handler.codec.decoderexception badly compressed packet

Is the server modded?

no, it is not moded the same thing happened to me today on hypixel

I just removed unwanted files at it works (just check the files you do not what to remove anything important)  

Can you please be more specific with the files you removed and what location were they stored(ie %appdata%/.minecraft)?

Please attach the full launcher log found in [minecraft/launcher_log.txt|http://hopper.minecraft.net/help/guides/finding-minecraft-data-folder/].
Also please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report (minecraft/crash-reports/crash-<DATE>-client.txt) here.

I've got the same issue, but with more error messages. For example java.lang.RuntimeException: VarInt too big. I have also gotten som more, but i mostly get badly compressed package.

Note: It hapens on both realms, vanilla servers, and "moded" servers, if that makes a difference.

This might be a technical issue. If you get this error message, please go to Community Support (linked below), maybe they're able to solve this problem.

Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – 📖 Game Wiki

Happenning now on a very stable and broad wire connection, even on LAN, so it's not about network problems. 

I have had it on both modded and vanilla versions, mainly 1.15.2 (because I never actually played the other ones except for a little of 1.12.2). Was getting both "below" and "above" versions of it. And this bug is there for several years already, just try to google for "badly compressed packet". This looks like either a bug in netty or in how Minecraft interacts with netty.

On a modded Minecraft (Forge) I was able to reproduce it by adding certain mods, and removing them removed the problem. My guess is that at some point the amount of information for a chunk or a packet gets too high and Minecraft does not handle it in any way. This happens in both vanilla and moded Minecraft.

 PS: Also, any kinds of log, the client log, the launcher log, the server log – don't contain any mention of this exception at all, as if it had never happened.

EDIT: Just did a little more searching and apparently this problem originates from: https://github.com/ObelouixServer/Minecraft-1.12/blob/master/temp/src/minecraft/net/minecraft/network/NettyCompressionDecoder.java where the maximum packet size is hardcoded for 2mb (a guess since I can't know what the obduscated functions really do), which is a pretty weird hardcoded limit? Maybe that was a thing tens of years ago when Minecraft appeared, but is there any need in that today? The games and game worlds become more complex and having a lot of data is a norm.. Or maybe is there an error in packet encoding that creates malformed packets? That would be the only reason to justify that check to ever exist there at all. So what is it?

Just wanna throw in my two cents and keep this issue relevant. This just started happening to me today with Realms, version 1.15.2. Not sure if it matters, but I also just upgraded my PC hardware (like, all of it but the graphics card), and this is my first time on Minecraft since upgrading.

This can be caused by having too much data in a chunk. You can do /kill @e[type=item] to fix it as it might be an item entity that is causing it.

Please provide a repro case.