I have the same problem. I have been reading to try and fix it. I had three cases of disapearing Sims, I have Sims 4 limited edition (the cd) not downloaded. Anyway, I created a family of a single male elder Sim, put him in a house and later that evenving went back to the house after leaving it to manage other sims to find him completley gone, as if he never existed. Yes I saved.
The next day when I turned on the game, I went to play with the "GOTH" family and the father vanished, no trace of him, he is not dead just vanished as if he never existed, which is strange because he is an EA created family that comes with the game. No relationships associated with him. Nothing.
My third disapearing act was a baby. One of my Sims had a baby, the baby came home, was there for 1 Sim day. I saved the game, went back to it later on in the evening and there was an icon of the sim child, as another user said, he looked nothing like the Sim parents.
My sims were redhaird, pale Sims and the child was asian with dak hair, but the strange thing was, the baby became a child within 1 sim day, but the "Child" never showed up in the game. You could click on the icon and assign actions but nothing would happen. The Sim was not on the lot, or off the lot, just gone. I knew it was a glitch, also a baby shouldn't become a child within 1 sim day, so i knew it was a glitch. I became frustrated and just killed the entire family off so that I could start over.
I have families who I play on a regular basis and I would be very sad if they disapeared because I have invested a lot of time in them and their houses. Sorry to vent but its so frustrating. 😕mileymad: