You have a few Windows Update failures, Make sure that Windows is updated properly (don't think that has anything to do with your issue but it's worth looking into nonetheless).
have you tried renameing your user folder yet ?
If not, Try the factory reset described in this post: http://answers.ea.com/t5/The-Sims-4/FAQ-Troubleshooting-Steps-amp-Known-Issues/m-p/3621199
You won't loose anything. Just make sure to not delete any files and make a backup.
After renaming, repair your game by right clicking on the game in Origin.
Try on a new game with nothing added back first (start new game). If it works, put back your save game and try again. If it still works, you can start putting stuff back.
The rest does not need putting back, cause they are mostly cache files that recreate or log files that are not needed for the game.
I don't work or have any association with EA. I give advice to the best of my knowledge and cannot be held responsible for any damage done to your computer/game.
Please only contact me via PM when asked to do so.
Hey so I was having the same problem and I figured it out. If you are in the manage world screen then select the household that you want to merge the pets with. In the bottom right hand corner (next to the play button) there’s the three dots, press the the dots and three other buttons will appear. Select the button that says manage household. A screen will appear and show you the household and give you some options in the bottom right hand corner again. Select the button that looks like a pencil to edit, add, or removed sims in CAS. Now it should take you to CAS mode. In the bottom left hand corner you can add a sim. Once you press that button the little menu will appear above it and you can add a sim from the gallery. Now you can select the household you wish to place right from the galley and they will appear.
August - last edited August
Having the problem as well. It seems that pets made after one of the gallery updates just won't load in CAS although you have them in your library. I experience it as well.