Im an idiot! Or at the very least I can be thick.

The bots work as I suspected... randomly. Muggins here got all excited when they looked like they were wierd. but there not.

In my defence I didnt get any warnings or errors when building the maps so how was I to know!

If you place a lava volume even slightly on top of a path node then the bot wont run in that direction... I mean their not thick are they why on earth would they happily run towards death (even if they cant see its there).

Im not sure if its because the lava volume is shouting to them "Im gonna kill you", or if its bacause the path node cant shout through the lava volume to tell them its their.

Either way my previous experiments turned up false results, the reason 3 directions were working was bacause in only 3 directions were the pathnodes free from blockages.
Heres what you coulda won...



anyhoo seems pretty random to me, I can make it un-random though by assigning paths different levels of importance, perhaps an important thing to do when attempting to create an illustration.