My sims disappeared!

I had a similar situation happen that I would like to add:

1. I have 4 families living in the neighborhood.
2. I switched from one while they were at work.
3. When I switched back, the sim icons were grayed out as if they were at work even though they were in the house and living. I just couldn't have any part in it.
4. I switched to a different house and instead of taking me to the house, it took me to the park. Again, sim icons were grayed out and I couldn't select them.
5. I fixed the issue by throwing a party and inviting the grayed out sims.
6. I switched families 3 times today.
7. The result being that one family completely disappeared from the neighborhood.
8. That family had family members living in 3 different places and anyone with that last name was removed from the game. The daughter who had gotten married and I manually changed her name was spared.
9. They are gone forever, not even in my library.
10. I did not do it. I went to manage the world so that I could move the last son into his own home when I realized they were gone. Their house still says they live there, but no family pops up. Then the other son who lives in a different house with his wife was also gone.

The biggest part of this whole thing is that anyone with the same last name as the disappearing family was also gone no matter what house they lived in.