(1) It can only be triggered every 15 mins. If someone has already triggered the mobs, no matter what you do, you will not get them to spawn
(2) Based on the order you trigger the pads (takes 2-3 people depending on which you are triggering) will cause different mobs to spawn. If you do it in the right order all three spawn at once and will get you the update. So if you get the order wrong and just trigger a normal spider or beetle or scrop, you will not get the update and you will have to wait another 15 mins
Step on scarabs (one player on each symbol) lights will disappear.
Step on spiders (one player on each symbol) lights will disappear.
Step on scorpions (one player on each symbol) lights will disappear.
Defeat the three bugs that spawn at once(a scarab, scorpion, and a spider)
Interact with the shields on the wall.
You should get a skill point and achievement.