[NEEDS SAVES] Partnered Sims turn into siblings/family relationships

Found a somewhat feasible workaround that doesn't require you to make your sims forget all their relationships, or replace them with "clones" from the gallery and lose their milestones etc. 

Move Partner A into a different household, change them in CAS there. Move them back. 
Move Partner B into a different household, change them there, move back. 
Do the same with the child. 

As soon as one partner + their child are still together, it removes the romantic possibility between both parents. 

I am having the same issue. Whenever I go into Cas to plan/change outfits or any other CAS parameters, my married sims can no longer perform romantic interactions, being treated by the game as if they were siblings. 

I tried planning their outfits from manage worlds instead of accessing CAS through live mode, but no difference. 

Tried vanilla (without mods) and with mods, no difference. 

Just noticed THIS issue as well when I moved my main sims’ ex-husband father of child back into the main sim’s house after the last update.

Product: The Sims 4
Platform:Mac
Which language are you playing the game in? Norsk
How often does the bug occur? Every time (100%)
What is your current game version number? SP45: 1assets.beta-sp45.25
What expansions, game packs, and stuff packs do you have installed? Everyone except the journey to Batuu
Steps: How can we find the bug ourselves? ?
What happens when the bug occurs? Every time I enter CAS mode with a mirror, my couple that are married becomes siblings...
What do you expect to see? The sims will should be able to change appearances without becoming siblings with their spouse
Have you installed any customization with the game, e.g. Custom Content or Mods? Yes
Did this issue appear after a specific patch or change you made to your system? Yes
Please describe the patch or change you made. I installed life and death expansion pack.

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Every time I enter CAS mode with a mirror, my couple that are married becomes siblings and its ruining my game completely .... 

Unfortunately just got the same bug on my male/male couple. I did go to cas to give them new outfits, but I didn't notice the change immediately, because I was too focused on their baby. I only noticed when they went on vacation and there was no option to woohoo. I thought it was vacation rental lot bug and tried again once they got home. that was when I finally realized they had a sibling relationship. I cheated it away, but they still can't do anything romantic. I do use mods, so I can't be off much help, but yeah, this is apparently still happening.

Upon reading some other posts, I assume it must be the stepchild problem in my case. One partner was an adoptive father. After some time, I made the other partner an adoptive father too and everything was fine. Then I went into cas and that forced the silbing relationship. I mean, it¨s good that I know about it now, but apparently it cannot be changed even with cheats.

I also have this issue, i do use mods, and i havent quite isolated what caused it yet, havent quite messed with it yet. all i know is that sometime after all my neighborhood teen sims grew up to young adults and my children grew up to teens, suddenly my (former) kids thought they were siblings with all the unrelated teens in their household. and the (former) teens could not do hardly any romantic interactions with their love interests without glitching the heck out. i found this thread and deleted their relationship and used cheats to redo it and it worked again. so im guessing they also decided they were suddenly siblings with their love interests ><   EVERYONE decided they were related lol. i did go into cas after aging everyone as the main household i was playing had the 2 main children i was playing and after aging them up i wanted to redress them.  so it is possible like with everyone else it was caused by CAS. 

I know its not super helpful, just wanted to add my Me too anyways.

This also happens if you try to edit families a certain way. I tried to give parents to Lia Hauata and the game kept trying to force other things. First, her mother was forced as her aunt. Then her two parents kept getting a sibliing bit added to them, even after I FINALLY successfully got them married.

I've had this happen twice, but I didn't realize it was linked to outfit changes. I don't remember making any. I've had it happen with 2 of my male couples - it doesn't seem to happen with hetero couples?

With No Mods, No CC 

My Married couple are fine until i go into Cas either from a mirror, dresser or from Manage worlds to edit their cloths or how they look and it doesn't matter if i just am editing cloths and not how they look or vice versa, hell i could be updating their toddlers cloths, and they can no Longer do anything beyond give each other Massages. my sims relationship with her wife changes as well, it adds sister to the list of Relationship. and her wife i pull from the gallery and is not even remotely related as they met in game and then built their relationship before getting married! im going to place screen shows of before i go into cas and after,

these screen shots are before i removed my CC but i did go threw and remove it after this , cleared my Cache and the problem persisted.