@mark-coniglio hi Mark. At this time I am not aware of any regression with the mentions plugin, which would usually point to some sort of configuration error.
Do you see any errors on the client side, in the browser dev tools?
When a user has a queued message waiting to be approved and receives a notification that it has been accepted, the notification appears as if it does not have a reference user (question mark): you can change this behavior and specify a specific user id ? (as I can do for welcome notifications)
Will be available in 1.18.4
https://github.com/NodeBB/NodeBB/issues/9855