Why does find session not work after first client come in the room?

Hi, I’m using UE 4.27.2 and trying to show rooms available on the list.

I succeeded to show session list and clients can join the session.

but once first client comes in the room, second client can’t find the session.

and also, the result of session find brings the right host name but wrong ping number like 9999.

anyone know why it happens?