Participants' pictures disappear with new connection icon

Anybody knows what is this connection indicator ?

This is a ninja icon. This is when there is no enough local bandwidth and the bridge stops sending video for that participant to the local one.

Thanks for your answer.
When you write “not enough local bandwidth”, you mean on the side of the receiver of that video OR on the side of the sender of the video ?
Another question : what do you mean by the “local one” ?

Normally on the receiver.

That it can be stopped only for the receiver not for all participants.

I asked the teacher to make a speed test exactely when these ninja icons are appearing.
The numbers seem good to me.

In addition, her class had only 8 to 10 participants !
What else could be the reason ?

This is on right?