Blizzard has disabled the Sunwell Plateau dungeon temporarily while fixing a serious bug in one of the encounters. Don’t worry, PTR 2.4 isn’t over and testing the Sunwell Plateau isn’t over either. Recently, Julian Morris (WoW Landscape developer) hinted there is PTR 2.4 for at least the next two months.
Daelo: We discovered a pretty obnoxious bug with the Lady Sacrolash and Grand Warlock Alythess encounter that is making the encounter much more difficult than intended. Until we get that bug resolved, we’re going to bring down the Sunwell Raid instance on the PTR. I have no ETA on the fix at this time.