[FIXED] Natural born hybrids bug out

@crinrict I created a female mermaid sim and try a baby with a vampire.

She gave birth to a twin , a hybrid vampire-mermaid and a normal mermaid.

@crinrict I didn't use any mod to create a hybrid at all.

This is my first time getting one.

Same, and I never used any mod. I have the exact same problem and now I see I'm not the only one.
My mermaid and vampire had triplets (one who is only a merman, and two who are vampire-merman hybrids ). The hybrids have all the mermaid related powers, need blood to survive, fear the sun and can use some vampire powers, but they can't evolve and get other powers and I can't edit their dark form or their merman form. So they are basically normal mermen with some vampire powers and can't swim during the day because of the sun burning them.
I tried with a mermaid and an alien: they had an alien-mermaid hybrid who has all the alien and mermaid powers. I can edit her alien disguise but this disguise is also used as her mermaid form in water (she doesn't have a tail and swims just like a normal human sim). So she is basically an alien with some mermaid powers.
I think the Island Living pack somehow allows the creation of hybrids (mermaid + alien/or vampire) but the different forms (dark form, mermaid form and alien disguise) are not compatible.
PS: I'm sorry for any mistake, I'm not a native english speaker. I hope my message can be of any use.

Product: The Sims 4
Platform:PC
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What is your current game version number? 1.52.100.1020
What expansions, game packs, and stuff packs do you have installed? Island Living, Get Famous, Seasons, Cats and Dogs, City Living, Get Together, Get to Work, Strangerville, Jungle Adventure, Vampires, Dine Out, Spa Day, Outdoor Retreat, My First Pet, Toddler + Kids, Bowling Night, Vintage Glamour, Backyard, Romantic Garden, Movie Hangout, Spooky, Perfect Patio, Luxury Party, Holiday Celebration
Steps: How can we find the bug ourselves? 1) First, have a mermaid sim in your household 2) Befriend a vampire 3) Click friendly interaction "Ask to Turn" 4) If successful, usual moodlets for transforming into a vampire occur 5) Your sim turns into a vampire, transforming nto his/her dark form 6) Your sim is both a mermaid and a vampire, and should have the vampire energy and hydration needs (for the most part no bugs/glitches here, your sim is still mostly functional as a mermaid and a vampire)
What happens when the bug occurs? Honestly I thought this was intentional since the merging of the vampire energy and hydration needs worked perfectly (with the exception of the power points disappearing), and since the mermaid was still able to swim perfectly fine and transform into her mermaid form despite being a vampire. Once entering CAS though, the mermaid form disappears and only the dark form shows (a real bummer since I would really like some vampire-siren hybrids).
What do you expect to see? I either expected for mermaids to be unable to transform into a vampire and perform those interactions, or for mermaids to have both a mermaid and vampire form in CAS if they were able to perform those interactions.
Have you installed any customization with the game, e.g. Custom Content or Mods? Not now. I've removed them.
Did this issue appear after a specific patch or change you made to your system? Yes
Please describe the patch or change you made. This is only possible with Island Living and the latest patch

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First Pic - Vampire-Mermaid in the ocean, burning, needs panel (with CC/Mods)

Second Pic - CAS Glitch (Vampire Dark Form, No Mermaid Form, With CC/Mods, Note the lack of the link forms icon)

Third Pic - Pics 1 and 2 but with Mods/CC removed (It would not let me edit skin tone, eye colour, etc.)