It seems quite a lot of these events are bugged. I have seen them disappear or constantly spawn back to back in one location with no timer. The ones in City of Alinor are constantly popping in and out of the visible spectrum and it seems there is no timer to how they spawn or get triggered. Potentially what happens is they spawn and de-spawn to fast because there is no wait time given to an instanced event spawn.
the instance system itself is a great thing but the proximity system and timer system connected to it needs a rework