Hello.
Since pre patch has started there is preety annoying bug in Legion Dalaran. This applies to all mages who completed their Class Hall Campaign in the past and have active Nightborne Soulstone on the top of The Violet Citadel. That thing on the top of The Violet Citadel killing Felwing Screechers.
Pre patch did something unknow with correlations I described above (falling Felwing Screechers) this making huge FPS drops nearly to 0 in some places around Dalaran. That combination making game to freeze for about 10 seconds.
To reproduce that. Take you mage who did fully mage Class Hall Campaign. Go to The Violet Citadel and stand near Image of Chromie. Now wait for the Felwing Screechers falling down by the roof. There is going to be huge FPS drop and game will freeze eventually.
This bug only applies to mages. I have no freezes on any other of my characters. Even my other mage who did not do the Class Hall Campaign have no game freezes.
I found temporary solution. Setting View Distance to 5 will stop FPS drops and there will be no more game freezes.
I hope this is a known issue and will be fixed.