Relationships dissapeared

@0756a23551b406f42794c1dcd0db7379 

I've not heard of that ever happening, but I do think there is a way to fix if you are not adverse to using a mod, at least temporarily.  MCCC has a feature that lets you make relationships that the game normally wouldn't in CAS even with the cheat on.  I used it when I moved families from one save to another where some members are in other households.  The only problem is when a sim has died and the ghost has been culled.  Those portraits will show as blank or not at all in the family tree.  Since you say the portraits still show, then you'll probably not run into that.  If you decide to use it though, you should start at the top of the tree and work down.  Setting some relationships will automatically set others.  Like if you set a parent/child relationship, the child's children will automatically be seen as grandchildren to the parent.  

Hope this helps.

@CGrant56 

Thanks for the reply, unfortunately as the issue is not that they are not related to each other anymore but that they no longer know/remember any other sims, as I wrote "the family tree is as it should be". (They still register on each other's family tree and they recognize two of my sims are grandfather and granddaughter but these two sims no longer "know" each other.)

It's not just family members either but they don't remember their boyfriend/girlfriends or friends etc. They need to introduce themselves again to sims like their mother, husband, or child. As I also wrote all of the clubs I've created are gone too.

@0756a23551b406f42794c1dcd0db7379 

What happens when they are reintroduced to each other again?  Do the relationships restore themselves or do you have to build them back up again?  An example of what I mean is when, say, a husband reintroduces himself to his wife, does the profile show them as married or do you have to get them remarried? Do the relationship bars go back to what they were or do you have to do friendly and romantic socials to build them back to what they were?

Since you use mods, MCCC does have an option where you can delete a sim's relationships but it is used on sims one at the time.  Afaik, it won't work on a global scale deleting all relationships for every sim in the save.  And it would have to be done deliberately by the player.  But there may be other mods that I don't know about that can do that.  So, if it were me, I'd take a good look at whatever mods you have just to be sure one of them didn't cause whatever has happened so it doesn't happen again.

But it just could have been something has gone wrong with the save or it got corrupted somehow.  It's hard to tell.

Hope this helps.

@CGrant56 

They do not restore themselves if they have a relationship that isn't shown on the family tree (friends, girlfriend/boyfriend, etc). Since the family tree doesn't seem affected they do not have to get remarried but girlfriends/boyfriends have to ask to be in a relationship again.

The bars are not restored either, and spouses do not manually get a romance bar.

As I wrote I have removed every mod and cc from my game to check if something fixed itself but it did not. 

I also noticed it didn't only remove all the clubs and my sims relationships but also every calender event I put in myself, it went back to the original version of the calendar despite me having edited it heavily.