does it have a foundation?
I had a pathing issue, my sims did the same thing as what you are describing.
Was finally able to figure out that somehow, don't know how, a plant was put under the house that interfered with the pathing.
I think I found it by tearing up the floor except in that grid area (it wouldn't let me do that) and creating a basement. I was then able to look up and saw the plant.
I know there is an easier way to see under the house, but don't remember what it is, how to do it.
Was there a fire there at one time? It could be seen as dirty and they are ticked off that it wasn't cleaned up. Had that happen also, didn't get one tile that has a stain on it, blended in, and that upset my sims.
Did you move all the counters in the area? I know you stated you moved things around, but if it is possible that a book, plate or something could have gotten between the counter and wall that would upset them.
Had a book get stuck where the stairs, wall and fridge was, ended up tearing it all up to find out the cause. Bookcase was against the wall but the book didn't show up when I moved it out of the way. It was tearing the wall out and finding it under the stairs with a part in the wall. It was the maid that was having the fit over the book.
Not sure if any of this will help, but it can be a weird reason, or just a stupid glitch. If you can, move the house to a empty lot, bulldoze the house at the old lot and then move it back. That may help also. Plus side is you will end up with double of all the items in your house that you can sell and have some extra cash for all the stress your sims had to deal with.
If you move your house, make sure the lot is the exact same size, if it is bigger you can't move your house back to the original lot.
Good luck in finding the cause
