I have a theory about Sonorous Coulding failing. It has failed for me a
few times (although I have NEVER been attacked my any lizard in CT :). I
noticed (and posted) my success in Unrest a few days ago. My only
failure was when a mob spawned right near me and immediately attacked.
Then today I read a post from someone who was in CT and looking at the
spawns in the Throne Room, they stated that 2 mobs walked in OR spawned
and saw thru their invis.

I know certain mobs can see invis, and that invis can fail, but neither
I nor the poster got "you feel yourself starting to appear".

It appears that sonorous clouding works on mobs that are in the zone
when it pulses, but mobs who spawn and have not had a "dose" (pulse) of
it can see thru it. Just ancedotal evidence so far, if anyone can add to
this, please do so.