I'm playing on PS5 and the Calico Lobster is the only critter left I need for the museum (still also need 1 fish, 1 shark and 1 bug)
I'm on Fall year 3 (been diving since Summer year 1 and cleared the ocean Summer Year 2) and I haven't seen a single one.
I've checked computer for the rough location, checked wiki and other guides and narrowed it down to the 20-30m depths.
I've laid traps from the cave in area 2 all the way to the undersea farm and all I catch are starfish.
Google Gemni once said that the Calico Lobster is bugged and doesn't spawn at night but as far as I can see it doesn't spawn in the day to compensate for this.
I have a similar issue with a blue butterfly that spawns in summer only on windy days.
Problem with this one is, Summer year 3 only had on windy day (on day 1) and never again.
It's annoying to have to wait a full in-game year for one bug.


