Can't find sessions on mobile hotspot

Hello,
I’m using the Unreal basic Session Nodes (with Null subsystem). Creating and finding sessions work perfectly when connected to a Wifi network. However, doing the same series of tests when the players are connected to a common mobile hotspot doesn’t work - Find Sessions doesn’t find the sessions.
Maybe it’s not considered a LAN ? Any idea is welcome. Thanks

You should check whether the mobile hotspot is allowing network access between connected clients on the required network ports. The connected clients are the same ones where everything works on the wifi connection, right ?