Strange Gaps on Modular Assets


so I´m having this really weird problem with modular assets not perfectly snapping together when spawned via blueprint.
These are pieces I created myself in blender and they are vertex snapped to be exactly 2m wide.
When I place them in the editor by myself they snap together perfectly and there is no gap in between (see front of “Pic4”).

But when I try to use them to spawn houses of certain height and width there are tiny gaps in the walls (see pictures below - e.g. back of “Pic4”).
The strange thing is that these gaps only occur on 2 (of 4) sides of the house (see pictures below), which is really weird because they are all spawned in the same manner (see the function picture below).
I run a ForLoop 4 times in the construction script and call the SpawnRow function each time with the direction rotating 90 degrees each time (being (1,0,0) in the beginning).
“Spacing” is set to 200.
The Location input shouldn´t matter here but essentially it´s just “Last Location” being offset by 2m in the new direction.
The “SpawnMesh” function is only adding an instance to a “hierarchical instanced static mesh component” (specified by the mesh inputs) with the specified location and rotation and a scale of 1.

I have created these kinds of spawners multiple times now (in other projects) and never had this problem before but this time it´s really weird, especially as this is the second version of the spawner using a slightly different logic/order of spawning and this is happening again… In essence these are only ForLoops spawning meshes so I´m really confused…

I have tested the editor plane with 100x100x0 dimensions and the same happens, so it´s highly unlikely that the problem lies within my mesh.
I then thought that it may be some weird bug with my cell shading but as you can see there are actual gaps visible when looking from the top in wireframe mode (see photos).
Therefore my blueprint has to be wrong somewhere but I can´t see any mistake and I can´t think of any reason why this would only happen on 2 sides if it was actually wrong.

The 2 sides with problems are the ones facing negative y and negative x direction (relative to the blueprint actor) if that could be somewhat relevant…

In the top down picture below you can ignore the larger gaps on the corners (they only occur because one of the materials isn´t two sided).

If anyone had a similar problem in the past or could think of an answer, I would greatly appreciate your feedback.
I start to think there is some really weird bug with this project but I find it too weird to actually believe that´s the case and this problem is really annoying to me as the gaps get really visible and jittery in the distance.

EDIT: I just migrated the BP to another project and the exact same error persists, so it´s not specific to my current project and now I´m completely out of ideas what could be the reason…

Kind regards,