Recently (within the last month about) there has been an issue for horde (maybe alliance), where zones with Call to Arms quests or invasions have an insane amount of lag. Upwards of the 7000 world ms variety. It is so bad that people have to zone out and try again later or turn off war mode to go quest in that zone.
I’ve also noticed this lag while joining large groups for the world bosses around azeroth.
Maybe there is an issue with the communication between multiple servers? Not sure, but either way the lag in the situations is unplayable and unbearable.
example: I am now trying to do the intro quests for nazjatar. My rogue was in war mode to start it, unbearable lag. Press one button and it takes 5-6 seconds to respond. I hearth, opt out of world pvp, go back and no lag whatsoever.