I’m new with posting a bug report, so let’s hope I’m doing this right.
This error appears while constructing a building with two floors:
As you can see, I tried leaving a hole in the second floor, so when the building is finished my hearthlings may climb up a ladder to the second floor. Everytime I try to let the program build a wall around automatic I get the following two Engine Errors:
Error 1:
develop-2666 (x64)
stonehearth/services/server/build/build_service.luac:222: assertion failed!
stack traceback:
[C]: ?
[C]: in function ‘assert’
stonehearth/services/server/build/build_service.luac:222: in function ‘_get_blueprint_at_point’
stonehearth/services/server/build/build_service.luac:225: in function ‘_fetch_blueprint_at_point’
stonehearth/services/server/build/build_service.luac:230: in function ‘_fetch_column_at_point’
stonehearth/services/server/build/build_service.luac:231: in function ‘_add_wall_span’
stonehearth/services/server/build/build_service.luac:199: in function ‘visitor_fn’
stonehearth/lib/build_util.luac:264: in function ‘grow_walls_around’
stonehearth/services/server/build/build_service.luac:199: in function ‘grow_walls’
stonehearth/services/server/build/build_service.luac:189: in function ‘cb’
stonehearth/services/server/build/build_service.luac:304: in function ‘do_command’
stonehearth/services/server/build/build_service.luac:189: in function <stonehearth/services/server/build/build_service.luac:188>
Error 2:
develop-2666 (x64)
c++ exception: lua runtime error
stack traceback:
It’s easy to reproduce just try buidling something similar and you get the error, I’m sure.
My workaround to this bug is, to place the walls by myself, as you can see the program tries to put walls around the hole in the floor too and that makes it hard for my hearthlings to reach the second floor at all 
I’m no native speaker so if anything is unclear please be patient and I try to do it better 
