I see the announcements all the time, but nothing pops.
The Sky turns red, the street MOBs disappear, and nothing else happens with the Zombies. With the Rikti, the ships pass over and drop bombs and one-shots your pets, but nothing else happens either. No Zombies or Rikti appear.
This was a group event where you did not have to group, kind of like GW2, but you could still have a blast, and if you grouped it was even more fun. I've been part of a Zombie/Rikti PUG that continued on to PUG the zone in CoHV, not once have I seen this happen in CoHH.
Note, I run on redside, and I'm an Altaholic and my highest charter is 16... or was 16.
Your level is why. You have to be level 25+ for zombies or Rikti to appear.
Yeah, I fought off a wave of them on PI about two weeks back and it went just like it always had. Haven't seen a zombie event yet though.
But hey, Summer Blockbuster - is that really going to be put on the shelf after July?