Procedural Minecraft Style World - Issues with not rendering hidden faces

So I’m adapting Sharp Accent’s Unity tutorial around a colony sim for UE4. The main sticking point was that there aren’t multi-dimensional arrays in UE, but I got around that AFAIK by using a dictionary with a vector key to access a node struct I created.

I’m trying to now only render the faces of the terrain which would be visible to the player, but for some reason, I can only seem to do it for the south facing quads? Which makes ZERO sense to me as the logic is identical.
Ie correct:


But these are using the same logic, just looking in different directions for their dictionary key node?

I’ve been pulling my hair out over this and trying various other configurations, but for some reason it just won’t work. Is there some weird limitation to dictionaries I’m not aware of?

The keys look ok to me. Are you sure you haven’t already used those keys for quads facing the other way? ( I mean you get to the same key by adding or subtracting ).