Questions on adds spawning mechanics/crowd control

Usara

For those who have tried MoL and know the second boss fight :

Adds spawn regularly on those bosses. When they spawn, a light of their corresponding color falls from the ceiling, and bam, here is the add.
Half of them are casters and the common mechanic to deal with them is having a DK chaining them in the corresponding part of the room, so those adds can be quickly nuked.

So now, the problem me and my guild encounter regularly : adds are almost constantly under CC Immunity, and thus, can not be chained (the ones that appear next to the bosses, to be exact)

So, where are those CCs the NPC break come from ? We asked people to pay attention to the skill they were using to attack them when the add is not in his correct position yet : no Caltrops, no Crystal Shard, no Vampire's Bane, no Crippling Grasp, no Comet/Meteor, etc...
Still, the adds spawning next to the bosses immediately CC break. So still no chain possible.

Alright. So next, we asked people to ignore the adds COMPLETELY until the DKs had them chained where we want them. Even then, break CC at spawn.
So what the hell ?
I filmed one of our last try, hoping to find the culprit. Maybe because we were tired, but it took us some time to identify the issue.

The adds appearing next to the bosses spawn WITH a snaring debuff. Where does this snare come from ? The only AoE on the battlefield were Elemental Walls (Fire, not Ice, just to be clear).

Until it finally hit us : could it be the snaring effect procing from DK's Ardent Flame abilities passive ? But no Ardent Flames were used when the adds spawned...
Or more exactly, no Ardent Flame abilities were used when the adds APPEARED.

Fact is, the adds are actually already there as soon as the falling lights appear, but can not be targeted since they are invisible.

You know what I mean, you encounter this mechanic elsewhere in the game : first boss of AA, the Warden of vICP (boss and its clones), Dragonstar Arena portals, Maelstrom Arena too (though the enemies in the portal can not be damaged, controls do work on them), and I'm sure I'm missing lots of other examples.

So what was happening to us ? DKs Fiery Breath (and morph) on the boss. No target. Cone wide. Adds are hit event though they are not there yet. It's an Ardent Flame ability : it puts the reduce speed debuff on them. So they break free as soon as they appear. So they are immune to the grappling chains.

I now have two questions arising from this observation :

First, I'm being told that Reduced Movement Speed IS NOT a breakable control for players - and thus no granting of CC immunity (I rarely go in Cyro so I asked PvP players).
BUT, NPC do consider it as a CC. And break it. And are granted CC Immunity.
Is this intended ?

And second, controlling adds that are "invisible til I finish my badass spawning animation" bug is old, I know, but did anyone at ZoS ever stated anything about it ?
I assume they did, because they did turn portal-spawning mobs immune to damage for VMA in opposition to VDSA. But they are still affected by controls.
Can we still hope for a fix in the future of this rather stupid unintended mechanic ?
@ZOS_GinaBruno @ZOS_JessicaFolsom @ZOS_KaiSchober

In the meanwhile, we'll ask our DKs to stop using Engulfing Flames too, I guess...