With my game, you build to survive the monsters. Well, during build mode, you get a selection of default blocks added on with bought ones. But when you rejoin the same server, no duplication! But if you were to carry your data onto another server and save that server’s data, you’re able to dupe blocks. But you might think, “Just delete their blocks when they leave,” but my game isn’t a “build freely” type of game, so blocks delete on leave would only be good for griefers, and I’ve seen a game that had the same system but didn’t have this block duping system.
I only thought of a build mode locking system where it locks onto that server if they left during build mode, but they can do that by rejoining another server with build mode and leaving to refresh their build mode lock, and if they did that unintentionally they can disconnect and rejoin the same server and not get their stuff. I also have a same server saving system, where I just save the job id.