This is the line of text in the email:
“The new user x was automatically silenced because multiple users flagged x’s post(s).”
In this instance the user was automatically silenced because the new user typed too fast - not because multiple users flagged the post.
(The site setting ‘Notify mods when user silenced’ is ticked.)
I had that happen recently on my forum, too. It was quite confusing, especially because the message tells you to check the review queue, which is empty.
Just happened. However, I made a lot of settings changes yesterday to help with the spam issue we have, and so I’m pretty sure this was due to one or more of the settings I changed. Reverting them for now.