What causes Hadronox to reset in Azjol -Nerub HC?

For most of the last year, I rarely/never had problems with Hadronox acting funky. But over the last week or so, it seems to be frequent for the Hadronox path event to reset for reasons I can not determine.

What has been happening: As you are killing the 3 waves of Crushers, you see the message 'Hadronox moves up the tunnel'. But after you kill them, she resets and stops moving.

One group I was in, one person said that bug is caused by players standing too far back (up the web). But another group had a person that said the opposite, that you needed to be way back to avoid the bug.

Does anyone know what behavior is actually the culprit for this bug? I would like to know where to position the mobs so that the group won't stand in a problematic place.

To be clear, this is not related to any attempt to do the achievement. This is just a normal group engaging the Crushers near where they spawn.

I've noticed that it seems more likely to happen if someone attacks the mobs using a ranged attack while standing on the platform or bridge.

Didn't seem to matter were we stood. We were doing normal mode nit heroic. But had same issue. Pull first crusher other 2 spawn and immediately attack. Once killed they all reset. Tried skipping them entirely, by jumping off the bridge to the stairs and then to the hallway. Running down quickly as to not have too many adds. Boss pulls poisons the crap out of us and tosses us around and we died. Didbt seem to matter what we did, whole fight buggy.