Gave birth, no baby
Okay so I have two couples living under the same roof, and the girls got pregnant at the same time, twice. The first set was two boys, everything was fine, nothing wrong. When they got pregnant again, nothing exciting happened until they gave birth. One gave birth to a baby girl. After the other's "giving birth" animation finished, her belly and pregnancy moodlet disappeared and she teleported a foot away. No second baby. Just an empty bassinet.
I unfortunately did not save at all today (shame on me) so there's no way of restarting without losing a bunch of skills. I just wanted to get this problem out there and see if anyone else has encountered this.
I should also add that I had testingcheats on and disabled need decay. No mods.
Nope, it was never resolved. I wound up just editing the family and adding a child that was randomized between the failed parents' genetics. I have since moved on from that family and have most likely deleted it. I have not tried anything similar, let alone duplicate it, and thus the problem has never arisen again.