When you try to send a message with length higher than 57 from a JJ2+ client to a vanilla server, the message in the packet gets cropped by the client, while the echo shown in the screen contains the original full message. This leads to player thinking that his/her message was sent correctly, while it did not.

There should be some sort of a warning/notice about the message getting cropped, or a more convenient solution is to restore the chatbox 57 character limit back when chatting on vanilla servers.

Why am I asking for such a fix in 2022?
Because there are some custom(dedicated) vanilla servers that are still being hosted and people use it to chat mostly.

https://imgur.com/a/jwImNp7

Packet:
https://imgur.com/5bR25LJ

This should be an easy fix. Thanks for letting us know!
ETA: Fix will be available in 5.10.