When logging into rcon, the server sends lots of commands to the client. Especially in mods, like ddnet7 or my F-DDrace mod the amount of commands that the server sends is higher. While the commands are sent, the server loses connection to the master server and even after all commands are sent it cant find the connection back to it. Same can happen on ddnet7 servers with many votes on a mapchange/ difficulty change (e.g. from novice to brutal).
@Learath2 had an idea: