This mission has been bugged like this from the beginning. Cannot reliably reproduce it either it happens sometimes and sometimes doesn't. Not just the wyverns either, can happen to all the spawned mobs.
While it makes no difference to me at 125. When I got to the part where I had to kill some drakes. 5 drakes were clumped together in each group I had to kill. It's supposed to be 1 at a time. If someone was doing this mission at a lower level, that would be problematic.
