Guild Wars 2

I run into this frequently — notice that Flame Legion and or dredge are invading an area in Diessa Plateau (part of the Flame & Frost content) ,but upon arrival I find that there are zero invaders still active, and no assault vehicle.

EDIT
No portals, either. Just an imaginary circle around the purported event area and a cog in the middle.

I have noticed that too especially around the one near the Nolan waypoint. The notice pops up but when you go over, nothing is happening.

Have seen this as well on FA.