Family relationships keep being changed, and I can't change them back

I have a similar or maybe even the same issue.

When I enter CAS and save changes, the relationship to one parent is changed to uncle/aunt. The game creates an unknown parent in the family tree. I tested this with and completely without mods. Even without mods, the bug kept happening after entering CAS and saving the changes. I have a big file with many households with many family relations connecting them (5th generation). I usually fix the relationship via MCCC, but my sim forgets every trait of their parent in the process. And I have to exit and reenter the household for the family tree to be fixed. The unknown proxy parent stays in the family tree as an uncle/aunt which doesn't look great in the family tree. It's really annoying, I even transfered all my sims to a new save, re-established every relationship from scratch from the first generation on (brought them back to life and killed them off again), just to find out, the bug happens everytime I enter and exit CAS. 

Interesting. So far I haven't noticed any faceless family members, but I haven't looked through all my households yet. I tried using MCCC as well to fix the issue, but even after doing it the broken family relationships remained. I plan to try a new save to see what happens, but I am hoping it ends up being fixable since this is the save file I've had since first getting thr game.

Having the same issue here!

It happened to me too and I havent been able to play. I got a storyline worked up for my sims and have created a big family that I wanted to become royalty. What triggers this glitch for me is definitively the secret child glitch where the affair partner turns into my main male sims half sibling through his mother. Its not the mods fault because I had tried deleting every mod and see if I can change the sim relationship with cas.fulleditmode and it wont let it change. Not even other relationships. Was going crazy until I came across this thread

I am having the same issue here. Cas.Fulleditmode won't work and my sim's partner has turned into her brother... with max romance level. If someone comes across a fix, please let me know!

It has happened to me several times, seemingly when I move households. One I've been playing for years, I moved in the same neighborhood but the family was growing and I needed a bigger home. While the "son" transferred fine, the twin infant daughters did not. They had no relationship with the family at all. I tried MCCC but adding a relationship isn't an option. I tried clearing the relationship and nothing. Tried clearing ALL relationships and nothing. Went into CAS to set them there but it says that one of the twins is recognized (doesn't work in game) and the other one is showing up twice in the family tree - once as the daughter of the father and not of the mother, and the other as the daughter of her own twin!

I don't want to delete these two sims as it's a family I've been playing for years but it seems like it's been spotty on whether or not it can be fixed in the other many times it's happened. Again, when I move a household, the relationship bork.

Came here wondering if anyone else had the issue and if they've found a solution or cheat that helped them fix what should never be broken.

i don't know if this came during the update or via the many fixs we've had since -- made a family of 2 Twin Teens bt notice in playing they're now listed as HalfSibs.  is there anyway to return them back to same parents (w/o mods)?  parents were never in family, new CAS.

Eng PC, All DLCs non-Maker

no mods/cc; never used

1.122.218.1030 DX11 64Bit

I have the case that the daughter of my sim is at the same time the stepdaughter and secret child which makes no sense. Cas.fulledit let me change her to daughter but it still shows as the same in the relationship menu.