Unable to connect more than two or three

Hello,
I have been using and promoting Jitsi for months
With one group of persons, when a third person joins the conference, the window of the second turns grey and shows micro and video turned off. I tried with a new room name and got the same result. here are the two links:

any idea? could it be linked to a type of device? here it arised on a web connexion with a telephone.

Were you using the app or the browser on the problem device? Is it just that device that cannot hear the others? The other two continue to see and hear each other?

One more point : did you see that I posted the same message as a comment to the following topic:

Some users no audio/video on meet.jit.si, but can text chat, Rest of users fine

Yes , I saw it, but my questions are still valid.

I thought I had answsered :

Where you using the app or the browser on the problem device?

The person having the problem was using the jitsi app on her cellphone, a Samsung of 2016

Is it just that device that cannot hear the others?

it seems that this person only was affected

The other two continue to see and hear each other?

Yes

I can add that the problem is new: we have been using Jitsi with this same group many times since april. The problem arised first on our December 15th.

Would you need more info?

3670_2.jpg