This just happened to me, I just made a post about it but didn't find this in time. It turns out that in profiles they are now listed as both spouses and uncle/neice. I am not sure how the uncle/neice relationship got there (they were definitely not related before).
I think it started when they adopted her brother. Her father in another household died, her brother was a toddler so I moved him into their household. There was an 'adopt' option while the husband was playing with him so I clicked it and it said that the todder was adopted by the household. Soon after, they had no romantic options except "offer massage'.
I know prior to the adoption they had been romantic, as she was pregnant when the adoption took place. I didn't notice the absence of romance interactions until I got a message that he was 'very dissatisfied" and I tried them and they were gone.
On her family tree they are spouses, but on his family tree, her deceased father is now listed as his brother, but there are no lines connecting them. Weirdly, their romance bar is still full.
In CAS.Fulleditmode they show up as spouses and there are no family relationship options listed in the drop down menu. I tried changing it to household members thinking maybe I could change it back or have them remarry but it won't change from spouses.
I can't figure out how to remove the uncle/neice tags under relationship. I'm still playing around with it but I tried moving lots, clear cache, repair game, etc. All the obvious things.
If you want I can share my file as soon as I figure out how to do it lol. I will look at the link tomorrow when I'm not so tired.