Yes, I have figured it out. You are onto something, Karen. I had the same thought when I noticed the neighbor's mailbox across the street had the same type of texture. Across the street is a house with a family that has four tombstones. I entered the lot and I saw the tombstone on the sidewalk across the street, but it looked more normal instead of like in the picture. I zoomed in and moved my mouse over it, and it said "Here lies Coral Oldie." Then I remembered. I had forgotten about this, but her tombstone disappeared a while back. I didn't know why, but I used the Lot Debugger to respawn her tombstone and put it back where it was. I thought no more about it and played several other lots in the meantime. I still don't know why her tombstone moved, but it must have reappeared at some point at the edge of the lot, and I never noticed it.
I was trying to see whether it was normal for lots to overlap like this. When I was trying to get rid of the object earlier, it said it was out of bounds, and I had to turn on moveobjects to place the stuck object remover. I noticed when I was at the lot across the street, there were fine lines demarcating their lot that included the sidewalk opposite their house. I could send the sims to walk out here, but could not place objects. When I went back to the other house, the lines appeared around the opposite sidewalk as well, so it appears as if they are overlapping. I guess this is normal, but it just never caused any problems before.
Then again, we could never see neighbors before until NL.
Thanks for all the ideas, everyone.
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