Reading the forum it appears that this meta has been bugged, and ignored, for years. As I am attempting to do the gloriously crafted 100 portal spikes achievement, I have been camping this event for a couple weeks now. Folke almost always stalls, no exaggeration, I would easily be comfortable with claiming a 90%+ non movement rate on the NPC. Sola is fairly reliable but probably has a 15% stall rate. Afia is the most reliable and I have seen her stall once.
This doesn't technically stall out the whole meta event as people then use their skyscales to damage the spikes to progress the event. The problem with this is that there is 0 opportunity to advance your portal spike count when this occurs. Adding to the issue is that since this occurs regularly, when there are groups of people doing the event, some will actually just go skyscale fire the portals preventing even a functioning lane from allowing portal spike progress.
I would like to suggest that a portal spike increment be added to some stage of each lane as well. Either in destroying the portal in any manner or perhaps in defeating the realm keeper that spawns after the portal is destroyed. This way even if the event is bugged or people use the skyscale to bypass the natural progression of the event, some progress can be made on this achievement.