For MMO games, there may be dozens of map levels. Thousands of players are on different maps. The architecture of UE4 is that each map needs to start a dedicated server separately. When players go from map A to map B, they will disconnect from the dedicated server for map A and establish a connection with the dedicated server for map B. Because two dedicated servers do not share GameIns and may run on different computers. The only GameIns with information comes from the player’s client. In this way, players can change their own gold coins and props when switching maps, while the ‘B map’ dedicated server may not be able to detect it.
So how to communicate effectively among the servers of MMO? For example, when a player moves from map A to map B, map A sends the player’s information to map B.
It includes a key to identify the player’s information, which is used to ensure that the player connected to the proprietary server ‘map B’ is indeed transferred from ‘map A’, so as to prevent hackers from trying to connect directly to the dedicated server ‘map B’.
When map B receives the player’s connection, it recreates the player’s Character and other Actors had this player owner according to the information provided by map A and compulsorily synchronizes it to the player. Make sure that there is no change in the player’s data before and after switching maps.
You will need to establish network connection between servers either by sockets and send data or some centralized master server that tracks those stats (server A send data on update server B reads it when player joins). First option requires C++, 2nd option is doable in Blueprints with HTTP and VaRest plugin, but you need to develop the server
MMO games systems heavily relay on databases so option 2 seams more natural. You need to remeber about case of player exiting on Map A and when he return it lands in Map B or even C for some reason, it better to have one place to read player stats.