reproduction

1. start a vanilla 1.20.1 server
2. in singleplayer, use a command block to give an item, where the nbt is > 256 character long (longer than you can paste in chat)
3. bookmark the item
4. join the server, op yourself (i think?)
5. try to spawn the item with ctrl + left click. ctrl middleclick seems to work as normal, except if in certain guis (crafting table)
6. observe that you disconnect from the server

error

in client console

https://paste.ee/p/2XkFT

on disconnect screen

version

quilt 7.0.3+0.83.1-1.20.1
minecraft 1.20.1
emi 1.0.4+1.20.1

This has been resolved in dev. It will be released along with the 1.20.2 port in the coming days.