(bug): Every time a new message is received in messenger in real-time it copies the previous 11 or so.

Summary

This bug is driving me nuts. Please fix it asap. Every time a new message is received in messenger in real-time it copies the previous 11 or so. It is copying both sent and received messages. I think it's treating it as if it's the first time the chat window has been opened, simply loading the previous 11 sent/received messages but not realizing that those previous messages have already loaded. It should only load the new message(s).

Steps to reproduce

1. Log in to your primary account in Chrome.
2. Log in to your secondary account in Firefox.
3. Send 13 numbered messages (test1, test2, test3, etc.) from your secondary account to your primary account.
4. Send a message from your primary account to your secondary account without closing the chat window.
5. Send another message from your secondary account to your primary account without closing the chat window.

Platform information

Chrome/Win10 and Firefox/Win10

What is the current bug behavior?

Every time a new message is received in messenger in real-time it copies the previous 11 or so.

What is the expected correct behavior?

It should only load the new message(s).

Relevant logs and/or screenshots

(Paste any relevant logs - please use code blocks (```) to format console output, logs, and code as it's very hard to read otherwise.)

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)