UE5 Impossible to work with other peoples - Multi user editing not working

Hi, thanks by advance for your answers.

6 h in a row, we try to connect using the Multi-user interface. On Ue5.
It work like a charm in Ue4 but not working when we try in Ue5.

Load the plugin > restart
Add a name, a color, and that :

Me
Unicast Endpoint : IP hamachi (IPV4)
Multicast Endpoint :
Static Endpoint : IP Him :

Him
Unicast Endpoint : IP hamachi (IPV4)
Multicast Endpoint :
Static Endpoint : IP Me :

work 1 times for 15 minutes, we reload the scene to verify again,
do not change anything and it never work again.

It never work if we do not use a VPN > hamachi
Sometimes we have error, sometime we do not have any, and when i do not get any error i can’t create a session.

We want to start on Ue5 together but at this instant after trying 6 hours …
we have no clues about how to fix this.

Any help will be more than welcome
Thanks