In Blood Moon, I noticed that when an enemy champion (I didn't see if it happened on allies, gonna check now) kills the herald, it often displays a blue square on top of their icon, and the message is not displayed, showing a "code" instead.
1- Queue up for Blood Moon
2- Enter a game
3- Have the enemy team kill the Herald (or Demon)
I'm still looking for how exactly the bug is produced, so I will update this post on my progress.
EDIT: I just noticed that the announcement error is also included in the chat.