[IL] Mermaid tail is invisible

I have the same problem now, the tail of my own mermaid Sim is visible, but when she goes into the ocean she meets other mermaid Sims with only a torso and no tail .. 

One of them even had a tail in one moment, and when i restarted the same save as i was just testing something unrelated he suddenly didnt have a tail. That same Sim, at the time when he had a tail in the ocean, I went into manage households and opened his unplayed houseold in CAS, there was no tail either in CAS, even though he just had a tail visible in the ocean!

It doesn't seem to be tail type related, as i had missing tails of the first category and then another Sim didn't have that same tail missing in the same category. I couldnt find a pattern though, what makes it disappear..

When I create a new household and add that same mermaid sim (with the missing tail in my game) from a backup copy in my gallery, his tail is still there. It looks like playing the game has removed his (and most of my other mermaids) tail. Some were not removed, I wonder if those were just not in the water recently as I rarely play with my mermaids or in Sulani.