Tonight our Operation team in 8 Man HM had Toth & Zorn down to 10% or just below, (they were around 1% hp apart of each other) when the leap happened the event reset itself.
This happened twice.
The other problem we ran into, seemingly around 3-4 times in a row was the Yellow Reticle for the Berserk-removing rock throw landing on the tank of Zorn - which is essentially an event-breaker.
This needs some investigation.
Zorn is perma rooted during the toth enrage phase, so there shouldnt be to many issues with the tank running up to toth. From a healer on toth perspective, i find it easier when the second tank gets the yellow, since he/she can migrate the damage from the shockwave far easier then someone in light armour, which requires a mass amount of healing.