BungeeCord: Server unreachable

People can't join to a certain server when they try to join (using a portal or/and command to get connected to the server). When they try to reach the server they don't get connected to it, after a few seconds of typing the command to get teleported to the server or using the server portal in the hub, they get the following:



I can connect to the server experiencing this issue directly without BungeeCord, the problem is only happening when you try...

BungeeCord: Server unreachable