In rare cases, different worlds may not have unique identifiers within the server network. To rule out the possibility of this, the BungeeCord/Velocity plugin "combine" the world ID from the downstream server with the name of same server. That's why I recommend installing the plugin on both proxy and the server.

Most of the time servers send completely unique IDs that can be sent to players as-is.

We may try to implement the solution that wouldn't change the world ID if it's already unique.

What do you think?