my process is almost exactly the same as yours, but i let the mobs reset all the way into the tower. i doubt that makes a difference though. my best guess: someone in your party was resting. make SURE everyone's standing when you pull or you might nip someone w/ rest aggro and make for a very bad day. not sure what else it could be unless maybe you're aggroing the mobs before you hit them. this paragraph was pulled directly from my attestation lecture for my LS, written up myself, and when it's followed, we've never had issue with the pulls.

Originally Posted by
Spekkio Pontificates
Attestation mobs are much like eyes in that they will spawn several hydra when aggroed. They are also very unlike eyes in that they, to a degree, share hate with their master making pulling only the NM potentially exceedingly difficult. If the following steps are completed exactly as written, a clean pull IS possible, however complications exist on Dagourmarche (Bst/Drg/Smn) due to his pets. The most reliable way to pull all but Dag is to first have someone aggro the mob and let it summon all 6 of its escorts. Have everyone but the sacrifice stand FAR back so as to not aggro the pops. Have the sacrifice run a tad back so as to be able to be raised or at least safely tractored and die there. At this point, the NM and his 6 escorts are popped and standing at their pop. Another sac puller is needed to make this pull now. Have the sacrifice voke/shoot/or otherwise pull one of the hydra (NOT the NM! This is very important or the sac pull WILL fail!) and run to a safe place to die. Meanwhile, have ONE pld on hand near the tower to pull the NM from the tower to the campsite. The campsite must be away from the tower or you'll get a nasty hydra surprise when the train returns.
PS, that was dia and not diaga, right? one will work, one won't.