From the aforementioned link. They are aware and are working on it.

"Error 3001 Cause #1

A login cap is in place on every World in order to prevent them from going down due to high loads. Despite this, a number of extremely overloaded servers have allowed players to log in beyond this cap, resulting in the number of permitted lobby server connections to fail and cause Error 3001 and disconnect players in the queue.

・ Resolution for Cause #1

We currently have a general idea of what is causing this issue with extremely overloaded Worlds, and a fix is underway. However, these are areas where complex processing is carried out and careful fixing is required for this process. As such, fixing/confirming/implementation into the lobby server will require time. This will be implemented in the maintenance scheduled for December 8, and we are putting our full effort into it, but haven’t been able to determine the full details. Further details regarding this will be announced at a later timing as well."