I got Island Living yesterday, and I'm definitely seeing this with the Kealoha household that I'm currently playing. (*POINTS TO SCREENSHOT*)
I think those really dark spots are puddles of shallow water from the tide? (As I was typing this, though, I wonder if they're actually shadows, though...)
(I haven't played any other pre-made households, I just went into them long enough for the game to tag them as "Played.")
UPDATE: @PoptartJuniper pointed out on Discord that there's a sliver of the deck on that house that touches the water, and that triggers the swimwear change. I discovered that it's actually the stairs leading up to the house deck? I decided to try building a different set of stairs on the opposite side, and had the family manually go up them. No swimwear! (I attached a pic; the offending stairs that come with the house are on the opposite side.) I'll have to experiment some more with that, but hopefully moving the stairs helps alleviate the issue in that lot, at least.
It's a shame this bug has never been fixed, it's pretty annoying.
From what I've seen it only happens on waterfront lots depending where the stairs are, if the stairs are placed too far back the game thinks your sim is going into the sea when they're actually going up the stairs.Only way round it is to edit the lot and bring the stairs further forward which is a pain to do and often ruins the look of the lots
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