Random problem of remote connexion but OK in LAN

Hello and sorry for my poor english
I’ve installed a jitsi-meet server a few days ago
It works perfectly in p2p mode (2 users) whether LAN or remote
It works perfectly in JVB mode (3 or more) in LAN but fails randomly, about 3 times out of 4 when someone connects from the outside: the person is connected, we all see his presence, but no video or audio
To connect, you have to insist, sometimes 7-8 times before it ends up working, just by hanging up and reconnecting.
We are using a VDSL connection, 40 mb down and 10 mb up, which is not saturated.
A priori all the ports are redirected as it should.
What can i do to fix this?
Thanks a lot

How did you manage to get p2p mode when on remote? I get it on LAN, but not on remote.
Did you configure something about stun?

no idea
We just noticed that two of them still work, both locally and remotely, so we deduced that we were in p2p mode.
Here we have completely disabled p2p mode to avoid that if a 3rd connects locally, it cuts the remote connection.
Suddenly, even only two, it uses JVB directly and therefore, remotely, the connection always fails 3 times out of 4