Did someone make an insignificant change that shouldn't have effected anything before the downtime, and it broke everything?
There was a live server issue that is causing this. As Wrel mentioned, Ops is troubleshooting and should have it fixed soon. No characters have been harmed, or lost, in this incident.
Ops department is looking into this issue right now. We'll let you know when we've got an update.
The "data migration" reference is probably TMI and will cause widespread panic, but for the sake of transparency, we wanted to provide a bit more detail than just "servers coming down for maintenance for up to 12 hours!".
That said, its literally a necessary database maintenance that just needed to happen. And given the time required, it there would be no ideal window that didn't impact someone's prime time.
This particular maintenance will not need to happen again for a long time.
Friendly reminder for those uninformed that walljumping has been explicitly okd by the devs - it is not a bug or exploit and instead is emergent gameplay
Can confirm, we do not consider this an exploit.
Another tip is that if your 10 year old PC's framerates aren't high enough, you can scale the wall while looking down, or away from the battle (and even climb it backwards) since you will have better framerates while you do it.