Hi! I had this problem as well! Where no horses were showing up in game but I could create them in CAS but they wouldn't be in game afterwards. Even the horses that were with the premade families in Chestnut Ridge disappeared! I came across this thread while searching trying to figure out what the problem was & after spending the past couple hours I believe I FINALLY FIXED IT! So, I thought I would come back & share with y'all what all I've done just incase it might help!
*[I PLAY WITH MODS & CC]*
After updating my game..
1. I updated any mods that had been updated so far & removed any broken mods!
[ ⇨HERE and HERE ⇦ ] are two sites that I always refer to see what mods have been updated and/or broken after each updates! ]
2. I deleted "localthumbcache" that is located in The Sims 4 Folder [not Mods folder]
[If you don't play with any mods or cc, I would suggest trying to repair your game and/or delete the "localthumbcache" in The Sims 4 folder if you haven't already!]
[Also, I will add that I did notice someone above said that the Mod More Traits in CAS by thepancake1 and MizoreYukii is NOT compatible with the Horse Ranch EP which is true! There is an update now & after updating it, I didn't realize at the time I didn't delete the OLD mod after my game loaded & it still seemed to be causing a little bit of an issue in my game. So.. just a little side note to always make sure you delete any OLD mods!] 😊
I hope this helps!❤️️
[This is just information I wanted to share with y'all from my own personal experience & what I've done that helped me with this issue! Use your own discretion!]