Two thoughts. There was one spot that would isntant repawn mobs in Loch Modan near a quest item. You really had to bring about 4-5 people to get it, cause they would respawn when killed in less than 2-3 secs and you didn't have enough time to get item open. So a few people would distract(pull) mobs and some even cheated and just tanked the mobs instead of killing them so they wouldn't respawn while the other people got the item and repeated it for the other people. Mobs were like 14-18, so not huge, but it just make a memory for me. I think Blizzard has added a new feature about 6 months ago or more when they saw 600000 people trying to start in Draenei and BE areas and wiping mobs wholesale. There wasn't enough mobs to do the starting quests. They come up with a mob killed respawn thingy. If more mobs are killed in an area that is used for quests (gnolls are used for quests) then the mobs respawn faster then normal. So could be 2 things, one, broken repawns or the game thinks there are more people there questing, so they respawn mobs faster. Either way, if you can deal with it, it is kinda action game fun.