I found this originally with mods when trying the Pack Legacy Challenge with only Outdoor Retreat, Laundry Day, Bust the Dust and maybe a couple other stuff packs and kits, so the only worlds were the base game ones plus Granite Falls. Since one of the mods was MCCC, I initially didn't know if it was a vanilla problem or a problem with MCCC. have now run into it again with mods disabled, eliminating the possibility that MCCC was moving people into the vacation rentals.
In my latest iteration, I have found a sim I wanted to add to my household since he had the trait I was looking for to proceed with the challenge (squeamish, a trait added in Outdoor Retreat so there are no default townies with the trait) and found that I could not invite him to my home lot, nor move with him in the base game worlds. Manage Households indicated he lived in Granite Falls. Going back on vacation in Granite Falls, I could move with him within Granite Falls. After a date, I got him to join my vacation, then join my household... but when I tried to move him into my household, I couldn't complete the move, I had to move my sim into his household. I then ended the vacation, and found my household at one of the vacation lodges, but without being able to access the interior of the lodge. Or rather, I could walk into the lodge, but there were no furnishings and only stubs of walls. I was able to move the household out of Granite Falls.
When I had earlier found this problem with mods enabled in a separate save, MCCC indicated that multiple people were living in the lodge I had rented. Checking Manage Households at that point, I found that a total of 13 households were living in Granite Falls.