First time in Dragon Soul and about half of the raid experienced the Green Fog permanently showing up when in the Dragonblight / Wyrmrest Temple areas. It even blocked out view of the Morchok and Ultraxion fight making it near impossible to see.
Same Problem, seems to go away randomly and come back randomly for players.
I was having this issue as well. I did have some luck but we were working heroics almost blind both figuratively and literally. The rest of my raid randomly got the issue but mine was persistent. I had just cleaned my cache and repaired game files before the raid. I don’t know if that was related. Lucky I played rogue and just had to time my feints on the 1st boss and stack on my tank that I could only see cause of the triangle marker they choose the put on him as a joke. I could randomly fix it rarely by running out the instance and counting to 15 and running back in but my next time zoning in would have the same issue. The fog also went away as soon as I walked into the temple in the middle. I disabled all my addons and the issue persisted. My network connection was unstable as well last night. I don’t know if that’s related just providing as much information as possible.