I was noticing that (seemingly random) failures of the purge would occur when the camp would spawn. You know the one, where you get the message that the purge can’t find a path to the coffer so it “retreats”.
As it turns out, I think I figured out what the issue was when not related to any actual obstruction to the coffer itself (e.g.: stairs being destroyed, etc.). It’s that sometimes when the purge spawns in an area where there are a lot of harvestable nodes, the demolishers can spawn inside those nodes and be trapped. Unable to move, the game decides the coffer is unreachable and gives up.
The simple and obvious solution seems to be that the purge should despawn all harvestable nodes in around the area where the camp is created. That would also prevent the situation where cages and chests are spawned inside large rocks, etc.
Of course, the workaround is to manually clear all debris around where purge camps may spawn, but that is a decidedly unfun exercise.