The Problem: 

When you destroy a shulker containing stacked tools or other stacked things that have large nbt tags, your client disconnects from the server and displays this message:

"Internal Exception: io.netty.handler.codec.DecoderException:
java.RuntimeException: Tried to read NBT tag that was too big;
tried to allocare: 2097185bythes where max allowed: 2097152"

reconnecting to the server loads the world as usual, but disconnects again after a fraction of a second in game. This results in a "quasi ban" and also affects everyone loading the area afterwards.

How to recreate:

1. Use something like NBT Explorer or the the "/more" command on a paper server with essentials installed to create a shulker full of stacked and enchanted items that you normally couldn`t stack. Now get that shulker into your creative saved toolbar.

2. Log into any minecraft server above 1.12.2.

3. Get the modified shulkerbox from your creative saved toolbar and place it on the ground.

4. Go into gamemode survival and break the Shulkerbox. After that you get kicked and get the error message. (no problem breaking it in creative)