This bug was fixed in Patch 1.47.51
My Sim has vanished from my save game. He’s not in the family tree nor anywhere else to be found. He was an child of Father Winter. All other Sims are still there.
A Bug in Patch 1.47.49 removes all children of father Winter from the game.
Currently there’s none. I would recommend to not load any save games that have children of Father Winter with the patch.
If you have already done so and also saved your game, then it’s probably best to make sure you keep a backup in a safe place until the bug is fixed.