Just layer manager saying its too busy so they needed to offload some peeps and won’t let anyone back in.
The layer manager is a system that controls layers, spins them up as needed, and decides which layer players logging in will be assigned to. The layer manager will try not to move you to a new layer unless certain thresholds are crossed. In normal times outside of major events and launch windows, this almost never happens.
When the world begins to fill on an individual layer and that layer begins reaching a critical mass however, the system may at times try to load balance the population on that individual layer to an existing layer or a brand new layer if all others are full, which at times means moving people onto a relatively empty layer. The layer manager system does have some safeguards to prevent you from too many jarring layering incidents, such as preferring NOT to move people that are in a group with each other, or that are in combat. Ideally, what will happen when a group is formed is that a re-evaluation will happen when people leave and join, and the layer manager will attempt to get everyone onto the same layer and keep them there until they all log out.
The snag we run into with the Battle of Ashenvale however, is that often times a great many people are joining groups, often times using external tools like discord to coordinate. When a player leader organizes several full raids to all congregate on one layer, that layer may hit a threshold and start trying to not add more people to that layer. For a time it will continue to allow more people to join to not break up groups, but there is a point when it reaches its absolute maximum and on the next evaluation the manager will forcibly move people off of the layer to balance the load and prevent a crash or other severe performance drops. This means that even players that were grouped and would normally be protected from being moved because they are grouped may also be moved as an emergency measure. This has been one cause for players unceremoniously being booted to a different layer; the layer simply got too full and stopped caring whether you were grouped or in combat or not.
Zone status is not maintained while switching layers and isn’t considered when moving players. You may however suggest that they should but I don’t think they do this as it may overload multiple layers at once decreasing overall realm stability.
But still worth a try.
Already happened during layering at Battle for Ashenvale.