Messages greyed out and don't send

Description:

Ever since updating to 3.12.3, messages will grey out and not send. The other person will get a notification sound, but not see the message. After restarting the server, the message will send, and all subsequent messages also send fine. But then after some hours to days, it will happen again, and I have to restart the server again.

Steps to reproduce:

1. Update to 3.12.3
2. Wait for messages to eventually grey out

Expected behavior:

Messages always properly send, as before

Actual behavior:

Messages grey out and don't send until server is restarted

Server Setup Information:

• Version of Rocket.Chat Server: 3.12.3
• Operating System: Ubuntu
• Deployment Method: docker
• Number of Running Instances: 1
• MongoDB Version: v3.6.3

Client Setup Information

• Desktop App or Browser Version: 3.12.3
• Operating System: Arch Linux, Fedora, Windows 10

Additional context

I remember this used to be a bug in a much older version, and it got fixed, so that might make it easy to fix again.

No source file, test, or entry point is identified. Reproduce the intermittent failure on Rocket.Chat 3.12.3 with the stated Docker and MongoDB setup, inspect server logs and messaging behavior before and after a restart, and use consistently delivered messages without restarting as the completion check.