[Open] Disappearing contacts and relationships of Sims

This issue happened to me a few months back so obviously the problem has not been solved.  Today, it happened again. This time I had started two different relationships with other sims in different households.  I then gave a party.  Now the relationships that I started before I gave the party are gone, and so is their households from my list.  This is very annoying and frustrating as one puts in the effort and time and it is wasted.