Eversong Woods: Rotlimb Cannibal raid on Fairbreeze Village event missing

As part of this event a group of 5 Rotlimb Cannibals (npc=15655) will spawn roughly at this location, where there is a conveniently empty space where there are no mobs spawning in, or patrolling through:

They will then proceed to run towards the Eversong Rangers and Ranger Sareyn in front of the broken walls at this location:

A short skirmish will ensue, they will get defeated, and the event repeats itself. The only details about how often are comments like "Every once in a while", so it's definitely not something which happens every 5 minutes.

Most sensible solution might be to have it on a 30 minutes timer and have it only happen once someone is actually there in the area and loads the grid, starting the event.